#!/usr/bin/env python3
import sys
input = sys.stdin.readline

n, k = map(int, input().split())
s = input().rstrip()
depth = [(0, 0)]
for ch in s:
    if ch == "(":
        depth.append((depth[-1][1], depth[-1][1] + 1))
    else:
        depth.append((depth[-1][1], depth[-1][1] - 1))
frm, too = depth[k]
if frm < too:
    for i in range(k, n+1):
        if depth[i] == (too, frm):
            print(i)
            exit()
else:
    for i in range(k, -1, -1):
        if depth[i] == (too, frm):
            print(i)
            exit()