#include <bits/stdc++.h>
using namespace std;
using ll = long long;
using llu = long long unsigned;

vector<ll> dx = { 0, 0, -1, 1};
vector<ll> dy = {-1, 1,  0, 0};

#define MOD 1000000007
int main() {
    int N;
    cin >> N;
    double sum = 1.5*N;
    int ret = (int)sum;
    cout << ret << endl;
    return 0;
}