import bisect import math import sys from itertools import accumulate from math import isqrt, inf from typing import List, Tuple sys.setrecursionlimit(10 ** 6) MOD = 998244353 int1 = lambda x: int(x) - 1 input = lambda: sys.stdin.readline().rstrip('\n') ii = lambda: int(input()) vi = lambda: list(map(int, input().split())) vi1 = lambda: list(map(int1, input().split())) def dbg(*args, **kwargs): print(*(repr(arg) for arg in args), *(f'{k}: {repr(v)}' for k, v in kwargs.items()), sep='; ', file=sys.stderr, flush=True) def main(): k, n = vi() d = vi() lsum = list(accumulate(d)) rsum = list(accumulate(d[::-1]))[::-1] for i in range(k): lc, ls = i, 0 if i == 0 else lsum[i - 1] rc, rs = k - i - 1, 0 if i == k - 1 else rsum[i + 1] ans = inf lx = (ls - 1) % n + 1 if ls - lx >= lc: ans = min(ans, lx) rx = n - (ls + d[i] - 1) % n if rs - rx >= rc: ans = min(ans, rx) print(-1 if math.isinf(ans) else ans) def _start(): if (ret := main()) is not None: print(*ret) if isinstance(ret, List) or isinstance(ret, Tuple) else print(ret) if __name__ == '__main__': _start()