def min_operations_to_make_good(s):
    n = len(s)
    operations = 0
    s_list = list(s)
    
    for i in range(n):
        zeros = ones = 0
        for j in range(i, n):
            if s_list[j] == '0':
                zeros += 1
            else:
                ones += 1
                
            if zeros > ones:
                for k in range(i, j + 1):
                    if s_list[k] == '0':
                        s_list[k] = '1'
                        operations += 1
                        zeros -= 1
                        ones += 1
                        break
    
    return operations

n = int(input())
s = input().strip()
print(min_operations_to_make_good(s))