def min_operations_to_good_string(S):
    N = len(S)
    ones = S.count('1')
    
    if ones == 0:
        return 1
    
    max_zeros = 0
    current_zeros = 0
    
    for char in S:
        if char == '0':
            current_zeros += 1
        else:
            max_zeros = max(max_zeros, current_zeros)
            current_zeros = 0
    
    max_zeros = max(max_zeros, current_zeros)
    
    if max_zeros >= ones + 1:
        return max_zeros - ones
    else:
        return 0

if __name__ == "__main__":
    N = int(input())
    S = input().strip()
    print(min_operations_to_good_string(S))