#!/usr/bin/env python3
# -*- coding: utf-8 -*-
"""
Created on Tue Nov 12 15:32:21 2019

@author: fujimotokohsei
"""

a=int(input('数字を入力してくだい:'))
b=int(input('数字を入力してくだい:'))

n=a*b

if n/100>1:
    print(-1)
else:
    print(n)



