n,m=map(int,input().split())
a=list(map(int,input().split()))
x = [ i for i in range(n,0,-1)]

for i in range(m):
    t=a[i]
    tt = []
    for i in range(t):
        tt.append(x.pop())

    for i in tt[1:]:
        x.append(i)
    x.append(tt[0])

print(x[-1])