i do not understand that neither
:'(

X first time
Y second time

1min XX
2min XY
3min YY

I think 2*n/k,
int main(int argc, char* argv[])
{
    int n, k;    cin>>n;    cin>>k;
    cout<<n*2/k<<endl;

    return 0;
}
but it's WA...