#include<bits/stdc++.h>
using namespace std;
#define int long long
int n; 
signed main()
{
	//freopen("ice.in","r",stdin);
	//freopen("ice.out","w",stdout);
	scanf("%lld",&n);
	int l=1,r=n;
	while(l<=r)
	{
		int mid=(l+r)>>1;
//		cout<<mid<<endl;
		if((mid+mid/2)>=n) r=mid-1;
		else l=mid+1;
	}
	printf("%lld\n",l);
	return 0;
}

求互关