#!/usr/bin/env python3
n, c = map(int, input().split())
a = list(map(int, input().split()))

done = 0
ans = (10**18, 0)
for i, x in enumerate(a):
    done += x
    done = max(done, c * i)
    t = done // c
    if t < n and t - i < ans[0]:
        ans = (t - i, i)
if ans[0] >= n:
    print("impossible")
else:
    print(ans[1])