def min_operations_to_good_string(n, s):
    operations = 0
    i = 0

    while i < n - 1:
        if s[i] == '0' and s[i + 1] == '0':
            # Start of a block of violating 0s
            start = i
            while i + 1 < n and s[i + 1] == '0':
                i += 1
            length = i - start + 1
            operations += (length + 1) // 2  # ceil(length / 2)
            i += 1
        else:
            i += 1

    return operations


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