#include<bits/stdc++.h>

using namespace std;

int main(){

int x,y,s=1000,m=-1;

cin>>x>>y;

int i=0;

while(i<=s){

	if(i%x!=0&&i%y!=0)
  
	{
  
		if(i>m) m=i;
    
	}

	i++;

}

cout<<m;

return 0;

}