#include<bits/stdc++.h>
using namespace std;
int main()
{
    double n,m;cin>>n>>m;
    int y=n/10*m;
    int g=y%10;
    if(g>=5)
    {
        y=y+10-g;
    }
    else y-=g;
    cout<<y;
    return 0;
}