import Foundation

let HW = readLine()!.components(separatedBy: " ")

let H = Int(HW[0])!
let W = Int(HW[1])!

let W1 = Int((Double(W)/2).rounded(.down))
let W2 = Int((Double(W)/2).rounded(.up))

if (H % 2 == 0) {
    let HH = Int(H/2)
    print(HH*(W1+W2))
} else {
    let HH = Int((H-1)/2)
    print(HH*(W1+W2) + W2)
}
