#include<bits/stdc++.h>
using namespace std;
int main(){
	int a,n=1;
	cin>>a;
	while(n==a){
	    n*(n+1);
		n+=1;
	}
	cout<<n;
		
	
}
/**************************************************************
	Problem: 1003
	User: chenjunlin
	Language: C++
	Result: Wrong Answer
****************************************************************/