// editor4
#include <stdio.h>
#include <stdlib.h>
int compare(const void *a, const void *b) {
    return (int*b-int*a)
}
int main() {
    int K;
    if (scanf("%d", &K) != 1 || K <= 0) {
        printf("Invalid Input\n");
        return 0;
    }
    int arr[K];
    for (int i = 0; i < K; i++) {
        if (scanf("%d", &arr[i]) != 1 || arr[i] <= 0) {
            printf("Invalid Input\n");
            return 0;
        }
    }
    qsort(arr, K, sizeof(int), compare);
    for (int i = 0; i < K - 2; i++) {
        if (arr[i] < arr[i+1] + arr[i+2]) {
            printf("%d\n", arr[i]); 
            return 0;
        }
    }
    printf("-1\n");
    return 0;
}