codility FrogRiverOne

Question:codility Lesson4 FrogRiverOne

My answer:

def solution(X,A):    B = [0] * (X + 1)    sumA = 0    for i in range(len(A)):        if B[A[i]] == 0:            B[A[i]] == 1            sumA += 1        if sumA == X:            return i    return -1