MAX = 1000

def replace_spaces(string):
    string = string.strip()
    i = len(string)
    space_count = string.count(' ')
    new_length = i + space_count * 2
    if new_length > MAX:
        return -1
    index = new_length - 1
    string = list(string)
    for f in range(i - 2, new_length - 2):
        string.append('0')
    for j in range(i - 1, 0, -1):
        if string[j] == ' ':
            string[index] = '0'
            string[index - 1] = '2'
            string[index - 2] = '%'
            index = index - 3
        else:
            string[index] = string[j]
            index -= 1
    return ''.join(string)