// yukicoder: 371 ぼく悪いプライムじゃないよ // 2019.6.17 bal4u #include #include typedef long long ll; #define MAX 130000 #define SQRT 360 char notPrime[MAX+10] = {0,0,0,0,1}; // zero: if prime void sieve() { int i, j; for (i = 3; i <= SQRT; i += 2) { if (!notPrime[i]) { for (j = i * i; j <= MAX; j += i) notPrime[j] = 1; } } } ll L, H; int check(int i) { int j = (int)(H / i); if (!(j & 1)) j--; while (j > i && notPrime[j]) j -= 2; if (j > i && (ll)i*j >= L) return j; return 0; } int main() { int i, j, f; ll a, ans; scanf("%lld%lld", &L, &H); ans = H - (H & 1); if (H <= 8) { printf("%lld\n", ans); return 0; } if ((a = H / 3 * 3) == L && (L & 1)) { printf("%lld\n", a); return 0; } if (a > L && (a & 1)) ans = a; sieve(); i = (int)sqrt((double)H); if (!(i & 1)) i--; j = i + 2; f = 0; while (i > 2) { while (notPrime[i]) i -= 2; if ((ll)i*i >= L) ans = (ll)i*i, f = 1; if (!f && (a = i*(H / i)) >= L && (a & 1)) ans = a; if (H / i > MAX) break; if ((j = check(i)) > 0) { ans = (ll)i*j, f = 1; } if (f) break; i -= 2; } printf("%lld\n", ans); return 0; }