n, k = map(int, input().split())
s = list(input())

x = 1
l = []
for i in range(n):
    if s[i] == '(':
        l.append(x)
        x += 1
        
    elif s[i] == ')':
        x -= 1
        l.append(x)

y = l[k-1]

if k >= n//2:
    print(l.index(y) + 1)
else:
    print(n - l[::-1].index(k))