#include<cstdio>
#include<iostream>
#include<algorithm>
#include<string>
#include<queue>
#include<vector>
#include<functional>
#include<cmath>
#include<map>
#include<stack>
#include<set>
#include<numeric>
#include<limits>

#define all(x) (x).begin(),(x).end()
#define rall(x) (x).rbegin(),(x).rend()

using namespace std;
typedef long long ll;
typedef pair<int, int> pi;
typedef pair<ll, ll> pl;
typedef pair<ll, string> pls;

ll N, K;

ll prime(ll n) {
	if (n == 2)return 1;
	for (int i = 3; i <= sqrt(n); i++) {
		if (n % i == 0) return 0;
	}
	return 1;
}

ll gcd(ll a, ll b) {
	while (b != 0) {
		a = a % b;
		swap(a, b);
	}
	return a;
}

int main()
{
	cin >> N >> K;
	if (N % 2 == 0) {
		cout << N / 2 << endl;
	}
	else if(prime(N)){
		cout << 1 << endl;
	}
	else {
		ll ans = 0;
		for (int i = 1; i < N; i++) {
			ans = max(ans,gcd(i,N-i));
		}
		cout << ans << endl;
	}
	
	return	0;
}