#include<iostream>
using namespace std;
inline void citeste(unsigned long long int &a)
{
    do
    {
        cin>>a;
    }
    while(!(a>=0 && a<=1000000000000000));
}
inline int cmmdc(unsigned long long int a,unsigned long long int b)
{
    unsigned long long int c;
    if(a==0 || b==0)
        return max(a,b);
    while(b)
    {
        c=a%b;
        a=b;
        b=c;
    }
    return a;
}
int main()
{
    unsigned long long int a,b,i,j,dif=0,x,y;
    citeste(a);
    citeste(b);
    for(i=a;i<b;i++)
        for(j=i+1;j<=b;j++)
           if(cmmdc(i,j)==1)
             if(j-i>dif)
               {dif=j-i;
                x=i;
                y=j;
               }
    if(x==a && y==b)
        cout<<b-a+1;
    else
    cout<<dif;
}