#include <bits/stdc++.h>
using namespace std;
using namespace chrono;
#if __has_include(<atcoder/all>)
#include <atcoder/all>
using namespace atcoder;
#endif

int main() {
    int64_t n;
    cin >> n;

    cout << (3 * n / 2) << endl;

    return 0;
}