import math
number = int(input())
print(math.floor((3/4)*number*2))#include <iostream>
using namespace std;
int main() {
int n;
cin >> n;
cout << n / 2 * 3 << endl;
}1A - Theatre Square | 1614B - Divan and a New Project |
791A - Bear and Big Brother | 1452A - Robot Program |
344A - Magnets | 96A - Football |
702B - Powers of Two | 1036A - Function Height |
443A - Anton and Letters | 1478B - Nezzar and Lucky Number |
228A - Is your horseshoe on the other hoof | 122A - Lucky Division |
1611C - Polycarp Recovers the Permutation | 432A - Choosing Teams |
758A - Holiday Of Equality | 1650C - Weight of the System of Nested Segments |
1097A - Gennady and a Card Game | 248A - Cupboards |
1641A - Great Sequence | 1537A - Arithmetic Array |
1370A - Maximum GCD | 149A - Business trip |
34A - Reconnaissance 2 | 59A - Word |
462B - Appleman and Card Game | 1560C - Infinity Table |
1605C - Dominant Character | 1399A - Remove Smallest |
208A - Dubstep | 1581A - CQXYM Count Permutations |