#include "bits/stdc++.h"
// Custom Header <<<
#define ALL(x) x.begin(), x.end()
#define rep(i, s, n)      for(int i(s); i < int(n); ++i)
#ifndef YDK
#define eprintf(...)
#endif
using namespace std;
using i64 = long long;
using pii = pair<int, int>;
template<class A, class B>inline bool chmax(A &a, const B &b){return b>a ? a=b,1 : 0;}
template<class A, class B>inline bool chmin(A &a, const B &b){return b<a ? a=b,1 : 0;}
constexpr int INF  = 0x3f3f3f3f;
constexpr i64 LINF = 0x3f3f3f3f3f3f3f3fLL;
constexpr int MOD  = int(1e9) + 7;
// >>>

signed main()
{
    i64 n;
    cin >> n;

    cout << int(1.5 * n) << endl;
    return 0;
}

/* vim:set foldmethod=marker foldmarker=<<<,>>> : */