#include <bits/stdc++.h>
#pragma GCC optimize("Ofast")
using namespace std;
long long pow(long long base, long long to) {
  long long ans = 1;
  while (to > 0) {
    if (to & 1)
      ans *= base, to--;
    else
      base *= base, to /= 2;
  }
  return ans;
}
long long gcd(long long a, long long b) { return (b == 0) ? a : gcd(b, a % b); }
int vsum(vector<int> v) {
  int sum = 0;
  for (int i = 0; i < v.size(); i++) sum += v[i];
  return sum;
}
void div(int n) {
  int i;
  for (i = 1; i * i < n; i++) {
    if (!(n % i)) cout << i << " ";
  }
  for (i; i >= 1; i--) {
    if (!(n % i)) cout << n / i << " ";
  }
}
bool prime(int n) {
  for (int i = 2; i * i <= n; i++)
    if (n % i == 0) return 0;
  return 1;
}
int main() {
  ios::sync_with_stdio(0);
  cin.tie(0);
  cout.tie(0);
  int t = 1;
  while (t--) {
    int n;
    cin >> n;
    cout << 3 * n / 2;
  }
}
