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#include <bits/stdc++.h>
using namespace std;
// https://blog.csdn.net/gl620321/article/details/104907041/
/*
通过找规律可以得到，如果（p, q）=d=1(互质), 最大的凑不出来的数是a*b-a-b.
这个可以看作是一个定理
*/
int main() {
int a, b;
cin >> a >> b;
cout << a * b - a - b << endl;
return 0;
}
