N = int(input())
S = list(input())
R, M = map(int, input().split())

if N % 2:
    print(-1)
else:
    A = [(1 if S[i]== '(' else -1) for i in range(N)]
    s = sum(A)
    if s == 0:
        print(0)
    else:
        print(abs(s) // 2)