#include <bits/stdc++.h>
#define rep(i,n) for(int i = 0; i < n; ++i)
#define all(x) (x).begin(), (x).end()
using namespace std;
const int INF = 1145141919, MOD = 1e9 + 7;
const int64_t LINF = 8931145141919364364, LMOD = 998244353;
// const int dx[] = {1, 0, -1, 0, 1, 1, -1, -1};
// const int dy[] = {0, -1, 0, 1, 1, -1, -1, 1};

int main() {
    int64_t n; cin>>n;
    cout<<n*3/2<<endl;
    return 0;
}