#include<bits/stdc++.h>
using namespace std;
long long n,l=1,r,mid,ans;
int main(){
	cin>>n;
	r=n;
	while (l<=r){
		mid=(l+r)/2;
		if (mid+mid/2>=n){
			r=mid-1;
			ans=mid;
		}
		else l=mid+1;
	}
	cout<<ans;
}