#include <bits/stdc++.h>
#define FI first
#define SE second
#define PB push_back
#define ll long long
#define FOR(i,a,b) for(int i=a;i<b;++i)
#define ROF(i,a,b) for(int i=b-1;i>=a;--i)
#define YES(i) cout<<(i?"YES":"NO")<<endl
#define Yes(i) cout<<(i?"Yes":"No")<<endl
#define co(i) cout<<(i)<<endl
#define fcout cout<<fixed<<setprecision(10)
#define uni(i) i.erase(unique(i.begin(), i.end()), i.end());
#define all(i) i.begin(),i.end()
#define pint pair<int, int>
#define vint vector<int>
using namespace std;

const int INF=1e9+7;
const ll LINF=1e18;
const int MOD=1e9+7;
//const int MOD=998244353;

int main(){
	int n; cin>>n; co(n*3/2);
}