#include <iostream>
using namespace std;
int main()
{
    int a,b,mi,ma,sol,solm;
    cin>>a;
    cin>>b;
    sol=-1;
    if(b%a!=0)
    {
        mi=a;
        ma=b;
        sol=b-a+1;
        cout<<sol;
    }
    if(a==1)
    {
        sol=b;
        cout<<sol;
    }
    if((b%a==0)&&(a!=1))
    {
        solm=-1;
        for(int i=a;i<b;i++)
        {
            for(int j=b;j>i;j--)
            {
                if(j%i==0)
                {
                    sol=j-i+1;
                }
                if(sol>solm)
                {
                    solm=sol;
                }
            }
        }
        cout<<solm;
    }
    return 0;
}