N, K = map(int, input().split())
S = input()
lcount = 0
rcount = 0

if K <= N // 2:
    for i in range(K):
        if S[i] == '(':
            lcount += 1
        else:
            lcount -= 1

    i = N-1
    while lcount > 0 :
        if S[i] == ')':
            lcount -= 1
        else:
            lcount += 1
        i -= 1
    print(i+2)

else:
    for i in range(N-1, K-1, -1):
        if S[i] == ')':
            rcount += 1
        else:
            rcount -= 1

    i = 0
    while rcount > 0:
        if S[i] == '(':
            rcount -= 1
        else:
            rcount += 1
        i += 1

    print(i+1)