#include <bits/stdc++.h>
using namespace std;
inline int getn() {
  int sign = 1, num;
  char c;
  c = getchar();
  for (; c < '0' || c > '9'; c = getchar())
    if (c == '-') sign = -1;
  for (num = 0; (c >= '0' && c <= '9'); c = getchar()) num = num * 10 + c - '0';
  return num * sign;
}
int main() {
  ios_base::sync_with_stdio(false);
  cin.tie(NULL);
  int n;
  cin >> n;
  n = n + (0.5 * n);
  cout << n;
}
