SUMDIV HSGHN L12 V2 2020-2021

#define task "SUMDIV"

#include <iostream>
#include <cstdio>
#include <vector>
#include <algorithm>

using namespace std;

using ll = long long;

constexpr int N = 1e5 + 5;
int l, r;
vector<int> divisors;

void Read()
{
    cin >> l >> r;
}

void Sub_12()
{
    for (; l <= r; ++l)
        for (int i = 1; i * i <= l; ++i)
            if (l % i == 0)
            {
                divisors.emplace_back(i);
                divisors.emplace_back(l / i);
            }

    sort(divisors.begin(), divisors.end());
    divisors.resize(unique(divisors.begin(), divisors.end()) - divisors.begin());

    ll ans(0);

    for (auto i : divisors)
        ans += i;

    cout << ans;
}

void Sub_3()
{
    ll ans(0);

    for (int i = 1; i <= r; ++i)
        if ((l + i - 1) / i <= r / i)
            ans += i;

    cout << ans;
}

ll GetSum(ll l, ll r)
{
    if (l > r)
        return 0;
    return (r - l + 1) * (r + l) / 2;
}

void Sub_4()
{

    ll ans(0);

    vector<pair<int, int>> intervals;

    for (int i = 1; i * i <= r; ++i)
        if ((l + i - 1) / i <= r / i)
        {
            intervals.emplace_back(i, i);
            intervals.emplace_back((l + i - 1) / i, r / i);
        }

    sort(intervals.begin(), intervals.end());

    for (int i = 0, j = 0; i < (int)intervals.size(); ++i)
    {
        j = max(j, intervals[i].first);
        ans += GetSum(j, intervals[i].second);
        j = max(j, intervals[i].second + 1);
    }

    cout << ans;
}

int32_t main()
{
    ios::sync_with_stdio(0);
    cin.tie(0);
    cout.tie(0);
    if (fopen(task ".INP", "r"))
    {
        freopen(task ".INP", "r", stdin);
        freopen(task ".OUT", "w", stdout);
    }
    Read();
    if (r <= 1000 || r - l <= 1000)
        Sub_12();
    else if (r <= 1e6)
        Sub_3();
    else
    Sub_4();
}