N,K = map(int,raw_input().split())
s = raw_input()
for R in [range(K-1,N),range(K)[::-1]]:
    a = 0
    for i in R:
        a += 1 if s[i] == "(" else -1
        if a == 0:
            print i+1
            break
    if a == 0: break