import std.stdio, std.conv, std.string, std.array, std.range, std.algorithm, std.container;
import std.math, std.random, std.bigint, std.datetime, std.format;
void main(string[] args){ if(args.length > 1) if(args[1] == "-debug") DEBUG = 1; solve(); }
void log()(){ writeln(""); } void log(T, A ...)(T t, lazy A a){ if(DEBUG) write(t, " "), log(a); } bool DEBUG = 0; 
string read(){ static string[] ss; while(!ss.length) ss = readln.chomp.split; string res = ss[0]; ss.popFront; return res; }
// ----- ----- ----- ----- ----- ----- ----- ----- ----- ----- ----- ----- //

void solve(){
	int n = read.to!int;
	int m = read.to!int;
	
	X[] xs;
	foreach(i; 0 .. n){
		xs ~= X(read.to!int, read.to!long);
	}
	
	X[][int] xl;
	foreach(x; xs){
		if(x.a !in xl) xl[x.a] = [];
		xl[x.a] ~= x;
	}
	
	long ans;
	auto xh = new RedBlackTree!(X, "a.b>b.b", true);
	foreach(i; 0 .. m + 1){
		if(i !in xl) xl[i] = [];
		X[] xq = xl[i];
		foreach(x; xq) xh.insert(x);
		
		if(xh.length == 0) continue;
		X x = xh.front;
		xh.removeFront;
		ans += x.b;
	}

	ans.writeln;
	
	
}

struct X{
	int a;
	long b;
}
