Tim T

#include <bits/stdc++.h>

#define TASK "ft"

using namespace std;

#define fst first
#define snd second

typedef long long int64;
typedef pair<int, int> pii;

const int64 oo = 1e18;

int64 div_up(int64 a, int64 b) {
    return (a + b - 1)/b;
}

int main() {
    #ifndef ONLINE_JUDGE
    freopen(TASK".inp", "r", stdin);
    freopen(TASK".out", "w", stdout);
    #endif
    cin.tie(0)->sync_with_stdio(false);
    int64 n, m; cin >> n >> m;
    if (n <= m/n && n*n < m) {
        cout << "-1\n";
        return 0;
    }
    int64 maxd = min(n, (int64)1e6);
    int64 ans = oo;
    for (int64 d = 1; d <= maxd; d++) {
        int64 e = div_up(m, d);
        if (e > n) continue;
        ans = min(ans, d * e);
    }
    cout << ans << '\n';
}