a, b = map(int, input().split())
sq = list(input())

if sq[b-1] == '(':
    s = 1
    for n,i in enumerate(sq[b:]):
        if i == '(':
            s += 1
        else:
            s -= 1
            if s == 0:
                break
    c = b + n + 1
    print(c)
else:
    if a == b:
        sq.append('|')
    ls = sq[:b].copy()
    s = 1
    for n,i in enumerate(ls[:-1][::-1]):
        if i == ')':
            s += 1
        else:
            s -= 1
            if s == 0:
                break
    c = b - n - 1
    print(c)