/*************************************************** * Alex Palcuie * Romania - 2016 * alex [dot] palcuie [at] gmail [dot] com * http://blog.palcu.ro/ ****************************************************/ #include <algorithm> #include <bitset> #include <climits> #include <cmath> #include <cstdio> #include <cstdlib> #include <cstring> #include <ctime> #include <deque> #include <fstream> #include <iostream> #include <iterator> #include <limits> #include <list> #include <map> #include <queue> #include <set> #include <sstream> #include <stack> #include <string> #include <unordered_map> #include <unordered_set> #include <utility> #include <vector> using namespace std; const int N = 1<<10; const int INF = 0x3f3f3f3f; int gcd(int a, int b) { while (b) { int r = a % b; a = b; b = r; } return a; } int main() { int x, y; cin >> x >> y; int max_dif = y - x; for (int dif = max_dif; dif > 0; dif--) { int no_pairs = max_dif - dif + 1; for (int i = 0; i < no_pairs; i++) { int a = x + i; int b = x + i + dif; if (gcd(a, b) == 1) { cout << b-a+1 << "\n"; exit(0); } } } cout << "-1\n"; return 0; }