import Foundation
import CoreFoundation

#if swift(>=4.0)
prefix operator *
infix operator **: PowerPrecedence
precedencegroup PowerPrecedence {
    higherThan: MultiplicationPrecedence
    lowerThan: BitwiseShiftPrecedence
    associativity: right
}
#else
extension String {
    func split(separator separator: Character) -> [String] {
        return self.characters.split(separator).map{String($0)}
    }
    var count: Int {
        return self.characters.count
    }
    func uppercased() -> String {
        return self.uppercaseString
    }
    func lowercased() -> String {
        return self.lowercaseString
    }
}
extension Array where Element: Comparable {
    func max() -> Element? {
        return self.maxElement()
    }
    func min() -> Element? {
        return self.minElement()
    }
    func sorted(by areInIncreasingOrder: (Element, Element) -> Bool = {$0 < $1}) -> [Element] {
        return self.sort(areInIncreasingOrder)
    }
    mutating func sort(by areInIncreasingOrder: (Element, Element) -> Bool = {$0 < $1}) {
        self.sortInPlace(areInIncreasingOrder)
    }
}
extension Array {
    mutating func swapAt(i: Int, _ j: Int) {
        swap(&self[i], &self[j])
    }
    func reversed() -> Array {
        return self.reverse()
    }
    mutating func reverse() {
        self = self.reversed()
    }
    func enumerated() -> EnumerateSequence<[Element]> {
        return self.enumerate()
    }
    init(repeating: Element, count: Int) {
        self.init(count: count, repeatedValue: repeating)
    }
}
extension _ArrayType where Generator.Element == String {
    func joined(separator separator: String = "") -> String {
        return self.joinWithSeparator(separator)
    }
}
extension Range {
    func reversed() -> [Element] {
        return self.reverse()
    }
}
func stride<T: Strideable>(from start: T, to end: T, by stride: T.Stride) -> StrideTo<T> {
    return start.stride(to: end, by: stride)
}
prefix operator * { }
infix operator ** {
    precedence 155      // 乗除算より強く，ビットシフトより弱い
    associativity right // 右結合
}
#endif
func readInt() -> Int? {
    return Int(readLine()!)
}
func readStringSplit(by separator: Character = " ") -> [String] {
    return readLine()!.split(separator: separator).map{String($0)}
}
func readIntSplit(by separator: Character = " ") -> [Int] {
    return readLine()!.split(separator: separator).map{Int($0)!}
}
prefix func * <T> (a: [T]) -> (T, T)             { return (a[0], a[1]) }
prefix func * <T> (a: [T]) -> (T, T, T)          { return (a[0], a[1], a[2]) }
prefix func * <T> (a: [T]) -> (T, T, T, T)       { return (a[0], a[1], a[2], a[3]) }
prefix func * <T> (a: [T]) -> (T, T, T, T, T)    { return (a[0], a[1], a[2], a[3], a[4]) }
prefix func * <T> (a: [T]) -> (T, T, T, T, T, T) { return (a[0], a[1], a[2], a[3], a[4], a[5]) }
func **(lhs: Int, rhs: Int) -> Int {
//    return (0..<rhs).reduce(1){i,_ in i*lhs}
    return Int(pow(Double(lhs), Double(rhs)))

}
func **(lhs: Int, rhs: Double) -> Double {
    return pow(Double(lhs), rhs)
}
func * <Element> (lhs: [Element], rhs: Int) -> [Element] {
    return (0..<rhs).reduce([]){a,_ in a+lhs}
}
func *(lhs: String, rhs: Int) -> String {
    return (0..<rhs).reduce(""){s,_ in s+lhs}
}
//func gcd(x: Int, _ y: Int) -> Int {
//    return y>0 ? gcd(y, x%y) : x
//}
//func lcm(x: Int, _ y: Int) -> Int {
//    return x * y / gcd(x, y)
//}
let MOD = 10 ** 9 + 7

/*************** テストスペース ***************/

//arr.sort{$0.0==$1.0 ? $0.1<$1.1 : $0.0<$1.0}  // タプル配列のソート

/*************** メインプログラム ***************/

let (N, M) = *readIntSplit()
var tasks = (0..<10**5+1).map{_ in [Int]()}
for _ in 0..<N {
    let (A, B) = *readIntSplit()
    tasks[A-1] += [B]
}
var ans = 0
var que = [Int]()
for i in 1...M {
    for a in tasks[i] {
        que += [a]
    }
    que.sort(by: >)
    if que.count > 0 {
        ans += que[0]
        que.removeFirst()
    }
}
print(ans)
