D - M=ab（开根号）

void solve()
{
    int n, m;
    cin >> n >> m;
    int ans = 9e18;
    int limit = sqrtl(m);
    while((limit - 1)*(limit - 1) >= m)
        limit--;
    while ((limit + 1) * (limit + 1) < m)
        limit++;
    for (int i = 1; i <= limit+1; i++)
    {
        int t = (m + i - 1) / i;
        // debug2(t,i);
        if(t <= n && i <= n)
            ans = min(ans, t * i);
    }
    if(ans == 9e18)
        cout << -1 << endl;
    else printf("%lld", ans);
}