#include <iostream> #include <vector> #include <algorithm> #include <string> #include <map> #include <cmath> #include <queue> #include <numeric> #include <climits> #include <iterator> #include <iomanip> #include <stack> #include <set> #include <cstdio> #include <bitset> #include <functional> #include <tuple> #include <list> #include <deque> #include <sstream> using namespace std; const constexpr int INF = 1e9; #define FOR(i, a, n) for (ll i = (ll)a; i<(ll)n; ++i) #define REP(i, n) FOR(i, 0, n) typedef long long ll; typedef vector<int> VI; typedef pair<ll, ll> P; struct Less{ bool operator()(const pair<string, int>&a, const pair<string, int>&b){ if(a.first==b.first){ return a.second < b.second; } return a.first < b.first; } }; const constexpr ll MOD = 1e9 + 7; ll extGCD(ll a, ll b, ll& x, ll& y){ if(b==0){ x=1; y=0; return a; } ll d = extGCD(b, a%b, y, x); y -= a/b*x; return d; } ll GCD(ll a, ll b){ if(b==0) return a; return GCD(b, a%b); } int main() { int N; cin >> N; cout <<fixed << N*3.5 << endl; return 0; }