#include <iostream>

typedef long long ll;

int main(){
    ll L, K;
    std::cin >> L >> K;

    ll lb = 0ll, ub = 1000000000ll;
    while(ub - lb > 1){
        ll mid = (ub + lb) / 2;
        if(2ll * K * mid < L){lb = mid;}
        else{ub = mid;}
    }

    std::cout << K * lb << std::endl;
}