Codeforces 439A Devu, the Singer and Churu, the Joker

#include <iostream>
#include <cstdio>

using namespace std;

int main()
{
    int n, d, sum = 0, arr[120];
    scanf("%d%d", &n, &d);
    for(int i = 0; i < n; i++)
    {
        scanf("%d", &arr[i]);
        sum += arr[i];
    }
    if(sum + (n - 1) * 10 > d)
        puts("-1");
    else
        printf("%d\n", (d - (sum + (n - 1) * 10)) / 5 + (n - 1) * 10 / 5);
    return 0;
}