#include <bits/stdc++.h>
#include <string.h>
#define rep(i,n) for(int i = 0; i < n; i++)
#define srep(i,a,b) for(int i = a; i < b; i++)
#define all(A) (A).begin(),A.end()
#define MOD 1000000007
using namespace std;
using ll = long long;
using P = pair<int,int>;
using Graph = vector<vector<int>>;

int main(void){
	int n; cin >> n;
	cout << 15*n/10;
}