#define  _CRT_SECURE_NO_WARNINGS
#include <stdio.h>
#include <algorithm>
#include <utility>
#include <functional>
#include <cstring>
#include <queue>
#include <stack>
#include <math.h>
#include <iterator>
#include <vector>
#include <string>
#include <set>
#include <math.h>
#include <iostream>
#include <random>
#include<map>
#include <iomanip>
#include <time.h>
#include <stdlib.h>
#include <list>
#include <typeinfo>
#include <list>
#include <set>
#include <cassert>
#include<fstream>
#include <unordered_map>
#include <cstdlib>
#include <complex>
using namespace std;
#define Ma_PI 3.141592653589793
#define eps 0.00000001
#define LONG_INF 30000000000000LL
#define GOLD 1.61803398874989484820458
const long long MAX_MOD = 1e6 + 3;
#define REP(i,n) for(long long i = 0;i < n;++i)    
#define seg_size 524288
long long powering(long long now,long long now_go){
	long long ans = 1;
	while (now_go != 0) {
		if (now_go % 2 == 1) {
			ans *= now;
			ans %= MAX_MOD;
		}
		now *= now;
		now %= MAX_MOD;
		now_go /= 2;
	}
	return ans;
}
long long inv(long long now) {
	return powering(now, MAX_MOD - 2LL);
}
int main() {
	long long n;
	cin >> n;
	long long geko = (n * 3) / 2;
	cout << geko << endl;
	return 0;
}