#include <bits/stdc++.h>
using namespace std;

bool sushu(int n){
	int i;
	if(n <= 1) return false; 
	for(i = 2;i <= sqrt(n);i++){
		if(n % i == 0){
			return false;
		}
	}
	return true;
}

int main(){
	int n,i,c = 0,ma = 0;
	cin>>n;
	for(i = 2;i <= n;i++){
		if(sushu(i) == false){
			c++;
		}else{
			if(c > ma){
				ma = c;
			}
			
			c = 0;
		}
		
		if(i == n) ma = max(c,ma);
	}
	
	cout<<ma;
}


/**************************************************************
	Problem: 1587
	User: admin
	Language: C++
	Result: Accepted
	Time:298 ms
	Memory:2072 kb
****************************************************************/