#include <bits/stdc++.h>
using namespace std;
int main(){
    int res[300005];
    int n;
    scanf("%d", &n);
    int m[5001];
    for(int i = 1; i <= n; i++)
        scanf("%d", &m[i]);
    int f;
    for(int i = n; ; i++){
        memset(res, 0, sizeof(res));
        for (int j = 1; j <= n; j++)
            res[m[j]%i]++;
        f = 1;
        for (int j = 1; j <= i; j++)
            if (res[j] >= 2){
                f = 0;
                break;
            }
        if (f == 1){
            cout << i;
            return 0;
        } 
    }
    return 0;
}

#9 #10 #16 #17 TLE

#11 #12 WA