# -*- coding: utf-8 -*-

def main():
    a = int(input())
    b = int(input())
    c = [int(x) for x in input().split()]

    c.sort()
    y = []

    for i in c:
        if sum(y)+i < a:
            y.append(int(i))
            sum(y)

    else:
        ans = len(y)
        if ans > b:
            print("error")
        else:
            print(ans)

    pass

if __name__ == "__main__":
    main()