#include<iostream> #include<string> #include<string.h> #include<algorithm> #include<stdio.h> #include<cmath> #include<vector> #include<utility> #include<stack> #include<queue> #include<list> #include<bitset> #include<functional> #define FOR(i, a, b) for(int i=(a);i<=(b);i++) #define RFOR(i, a, b) for(int i=(a);i>=(b);i--) #define MOD 1000000007 #define INF 1000000000 #define PI 3.14159265358979 using namespace std; typedef pair<int, int> P; int main(void) { int n; cin >> n; cout << n*3.5 << endl; return 0; }