#include <iostream>

using namespace std;

typedef long long ll;

ll gcd(ll a, ll b) {
  if(!b)
    return a;
  else
    return gcd(b, a % b);
}

ll best = 1;

void check(ll a, ll b) {
  ll g = gcd(a, b);
  if(g == 1) {
    ll diff = b - a + 1;
    if(diff > best)
      best = diff;
  }
}

int main() {
  ll a, b;
  cin >> a >> b;
  for(int i = 0; i <= 1400 && a + i <= b; ++i) {
    for(int j = 0; j <= 1400 && b - j >= a + best - 1; ++j) {
      check(a + i, b - j);
    }
  }
  cout << best << "\n";
  return 0;
}