#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
typedef pair<int,int> pii;
#define pb push_back
#define mp make_pair
#define rep(i,n) for(int i=0;i<(n);++i)
constexpr int mod=1000000007;
constexpr int mod1=998244353;
vector<int> dx={0,-1,0,1},dy={1,0,-1,0};



int main(){
	cin.tie(0);
	ios::sync_with_stdio(false);
	ll n;cin >> n;
	n*=3;
	n/=2;
	cout << n << endl;
}