#include <iostream>
#include <cstdio>
#include <algorithm>
#include <string>
#include <sstream>
using namespace std;

long long a, b;

long long gcd(long long a, long long b) {
    if (b == 0) {
        return a;
    } else {
        return gcd(b, a % b);
    }
}

int main() {
    long long max_dif = 0;

    cin >> a;
    cin >> b;

    for (long long x = a; x <= b && x <= a + 1000; x++)
    for (long long y = b; y >= a && y >= b - 1000; y--) {
            if (gcd(x, y) == 1) {
                max_dif = max(max_dif, y - x + 1);
            }
    }

    cout << max_dif;

    return 0;
}