#include <stdio.h>
#include <stdbool.h>

// Function to check Triangle-like condition for all combinations
bool triangle_test(int arr[], int k, int idx) {
    // Need at least 3 numbers to check triangle property
    if (k < 3) return false;
    // Check all combinations that include arr[idx]
    for (int i = 0; i < k; ++i) {
        for (int j = i+1; j < k; ++j) {
            // Skip if i, j, or idx are the same
            if (i == idx || j == idx) continue;
            int a = arr[i], b = arr[j], c = arr[idx];
            if ((a + b > c) && (a + c > b) && (b + c > a)) {
                return true;
            }
        }
    }
    return false;
}

int main() {
    int k;
    // Read k
    if (scanf("%d", &k) != 1 || k < 4 || k > 10) {
        printf("Invalid input\n");
        return 0;
    }
    int arr;
    bool valid = true;
    for (int i = 0; i < k; ++i) {
        if (scanf("%d", &arr[i]) != 1 || arr[i] < 1 || arr[i] > 99) {
            valid = false;
            break;
        }
    }
    if (!valid) {
        printf("Invalid input\n");
        return 0;
    }

    int strongest = -1;
    // Check each energy drop if it passes the triangle test
    for (int i = 0; i < k; ++i) {
        if (triangle_test(arr, k, i)) {
            if (arr[i] > strongest) strongest = arr[i];
        }
    }
    printf("%d\n", strongest);
    return 0;
}