dsadsa

#include <iostream>

using namespace std;
int n,a,b;
int nwd(int x,int y)
{
    if(y==0)
    return x;
    return nwd(y,x%y);
}
int main()
{
cin>>n;
while(n--)
{
    scanf("%d%d",&a,&b);
 if(nwd(min(a,b),max(a,b))!=1)
    printf("-1\n");
    else
    printf("%lld\n",(long long)(a-1)*(b-1)-1);

}

    return 0;
}