---

import sys 
s = int(sys.stdin.readline()) 
n = int(sys.stdin.readline()) 
a = [(elem[::-1]) for elem in enumerate([int(sys.stdin.readline()) for i in range(n)], 1)] 
f = s 
u = 0 
for j in range(len(a)): 
    e, i = a[j] 
    if i > f and a[j][0] >= 0: 
        break 
    elif i > f and e <= 0: 
        continue 
    (u, f) = (a[j][1], f + e) if f + a[j][0] >= f else (u, f) 
print((f - n - 1) % (f - n))