def min_operations(n, s):
    # For each position, track the excess of 0s over 1s
    # in the suffix starting at that position
    suffix_balance = [0] * (n + 1)
    
    # Calculate the suffix balance
    for i in range(n - 1, -1, -1):
        if s[i] == '0':
            suffix_balance[i] = suffix_balance[i + 1] + 1
        else:  # s[i] == '1'
            suffix_balance[i] = suffix_balance[i + 1] - 1
    
    # Initialize an array to track the minimum operations needed
    # to make each suffix a good string
    min_ops = [0] * (n + 1)
    
    # Process the string from right to left
    for i in range(n - 1, -1, -1):
        if s[i] == '0':
            # If adding a 0 creates an imbalance, we need to convert it
            excess = suffix_balance[i]
            if excess > 0:
                # We need to convert this 0 to 1
                min_ops[i] = min_ops[i + 1] + 1
            else:
                # We can keep this 0
                min_ops[i] = min_ops[i + 1]
        else:  # s[i] == '1'
            # Adding a 1 always helps the balance
            min_ops[i] = min_ops[i + 1]
    
    return min_ops[0]

def main():
    n = int(input())
    s = input().strip()
    print(min_operations(n, s))

if __name__ == "__main__":
    main()