Finding the shortest positive integer which is not present in the list

def solution(arr):
    sorted_arr = sorted(arr)
    final_arr = [i for i in sorted_arr if i>0]
    min_val = final_arr[0]
    j = 1

    while True:
        if (min_val+j) in final_arr:
            j += 1
        else:
            res_val = min_val+j
            break

    return res_val

var = solution([-1,-2,-3,-4,-5,-6,1,2,3,4,6,7,8,9])
print(var)