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

const int N = 30;
const int M = 1e4 + 10;
/*
2
3 5

答案：
4

最大不能表示的应该是：3*5-3-5=7
四个不能表示的数是：1 2 4 7
*/
int f[M];
int w[N];
int res;

int gcd(int a, int b) {
    if (b == 0) return a;
    return gcd(b, a % b);
}

int main() {
    int n;
    cin >> n;
    for (int i = 1; i <= n; i++) cin >> w[i];

    sort(w + 1, w + 1 + n);
    int m1 = w[1], m2 = w[2];
    int M = m1 * m2 - m1 - m2;

    int g = w[1];
    for (int i = 2; i <= n; i++) g = gcd(g, w[i]);

    if (g > 1) {
        cout << "-1" << endl;
        return 0;
    }
    //完全背包一维写法
    for (int i = 1; i <= n; i++)
        for (int j = w[i]; j <= M; j++)
            f[j] = max(f[j], f[j - w[i]] + w[i]);

    for (int i = 1; i <= M; i++)
        if (f[i] < i) res++;

    printf("%d\n", res);
    return 0;
}