#include<bits/stdc++.h>
#include<math.h>
using namespace std;
int main()
{
    long long n,k,mod,div,ans;
    cin>>n>>k;
    mod = n%(2*k);
    div = n/(2*k);
    if(k>=n){
        cout<<10<<endl;
    }
    else if(mod==0){
        ans = 10*div;
        cout<<ans;
    }
    else if(mod<=k){
        ans = 10*div+5;
        cout<<ans<<endl;
    }
    else{
        ans = 10*div+10;
        cout<<ans<<endl;
    }
    return 0;

  }