#include <bits/stdc++.h>

using namespace std;

int main()
{
    long long A, B;
    cin >> A >> B;

    long long sol = -1;

    if (__gcd(A, B) == 1)
        sol = B - A + 1;
    else if (A + 1 <= B && __gcd(A + 1, B) == 1)
        sol = B - A;
    else if (A <= B - 1 && __gcd(A, B - 1) == 1)
        sol = B - A;
    else if (A + 2 <= B && __gcd(A + 2, B) == 1)
        sol = B - A - 1;
    else if (A <= B - 2 && __gcd(A, B - 2) == 1)
        sol = B - A - 1;
    else
        sol = B - A - 2;

    cout << sol << "\n";

    return 0;
}