#include<bits/stdc++.h>
using namespace std;
using ll = long long;
#define rep(i,m,n) for(int i=m; i<n; ++i)
#define repl(i,m,n) for(ll i=m; i<n; ++i)

int main(){
    ll N;
    cin >> N;
    cout << (N * 15LL) / 10LL << endl;
    return 0;
}