def min_operations_to_good_string(n, s):
    operations = 0
    balance = 0  # difference: ones - zeros

    for char in s:
        if char == '1':
            balance += 1
        else:  # char == '0'
            balance -= 1
        
        if balance < 0:
            operations += 1
            balance += 2  # we flip this '0' to '1', so net +2 to balance

    print(operations)

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