#include<cstdio>
#include<iostream>
#include<vector>
#include <cstring>
using namespace std;


long long int n,m,k,i,j,p,x,y,a,b,t,sol,dif;

long long int gcd (long long  int a,long long  int b )
{
  int c;
  while ( a != 0 ) {
     c = a; a = b%a;  b = c;
  }
  return b;
}



int main()
{
    //freopen("c.in","r",stdin);
    //freopen("c.out","w",stdout);

    scanf("%lld",&a);
    scanf("%lld",&b);
    dif=1000;
    for (i=a;i<=min(a+dif,b);i++)
    {
        for(j=b;j>=max(b-dif,a);j--)
        {
            if(gcd(i,j)==1 and i<=j)
            {
                sol=max(sol,j-i+1);
                //printf("%d %d\n",i,j);
            }

        }
    }
    printf("%lld\n",sol);


}