#include<bits/stdc++.h>

using namespace std;

void __init__(){
	ios_base::sync_with_stdio(0);
	cin.tie(0); cout.tie(0); 
	srand(time(NULL));
}

void solve(){
	int p; cin>> p;
	
	bool can[p + 1] = {};
	
	for(int i = 0; i < p; i++){
		can[(1ll * i * i) % p] = true;
	}
	
	int now = 0;
	
	for(int i = 1; i <= p - 1; i++){
		for(int g = 0; g <= 31; g++){
			if(can[((i - g * g) + p) % p]){
				now = max(now, g);
				break;
			}
		}
	}
	
	cout<< now;
}
	
int main() {
	__init__();
	
	//int t; cin>> t;
	int t = 1;
	int now = 1;
	
	while(t--){
		//cout<< "Case #";
		now++;
		solve();
	}	
}