def next(num, turn, memo):
    if num not in memo:
        memo[num] = (0, turn)
        return 0
    memo[num] = (memo[num][1], turn)
    return memo[num][1] - memo[num][0]


def solve(input, target):
    memo, n = {}, input[-1]
    for i, j in enumerate(input):
        memo[j] = (0, i)
    for t in range(len(input)-1, target-1):
        n = next(n, t, memo)
    return n


print(solve([16, 12, 1, 0, 15, 7, 11], 2020))
print(solve([16, 12, 1, 0, 15, 7, 11], 30000000))