def min_operations_to_good_string(n, s):
    operations = 0
    zero_count = 0
    one_count = 0

    for char in s:
        if char == '0':
            zero_count += 1
        else:
            one_count += 1
        
        # If 0s exceed 1s, we need to flip one 0 to 1
        if zero_count > one_count:
            operations += 1
            zero_count -= 1  # flip a 0 to 1
            one_count += 1

    print(operations)

# Reading input
if __name__ == "__main__":
    n = int(input())
    s = input().strip()
    min_operations_to_good_string(n, s)