#include <bits/stdc++.h>

//#include <ext/pb_ds/assoc_container.hpp>
//using namespace __gnu_pbds;

using namespace std;

#define int long long
#define IOS ios::sync_with_stdio(false); cin.tie(0); cout.tie(0);

const long long INF = 1e18 + 7;
const double EPS = 1e-6;
const int MOD = 1e9 + 7;
const int MAXN = 2e5 + 100;

int n = 1046527;

bool is_prime(int a) {
    if (a == 1) {
        return false;
    }
    for (int i = 2; i * i <= a; ++i) {
        if (a % i == 0) {
            return false;
        }
    }
    return true;
}

inline void solve() {
    int ans = 0;
    for (int i = 0; i < n; ++i) {
        if (n - 2 * i > 0 && is_prime(n - 2 * i)) {
            ans = max(ans, n - 2 * i);
        }
    }
    cout << ans << '\n';
}


int32_t main() {
    IOS;

    int tt = 1;
//    cin >> tt;
    while (tt --> 0) {
        solve();
    }
    return 0;
}