Submission #3889356

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Source Code Expand

#include <bits/stdc++.h>
using namespace std;

typedef long long int ll;
typedef pair<ll, ll> pll;

#define FOR(i, n, m) for (ll(i) = (m); (i) < (n); ++(i))
#define REP(i, n) FOR(i, n, 0)
#define OF64 std::setprecision(10)

const ll MOD = 1000000007;
const ll INF = (ll)1e15;

int main()
{
    ll A, B;
    cin >> A >> B;

    ll sum = 0;
    FOR(i, B + 1, A)
    {
        ll s = ((i * (i + 1) / 2) % MOD) * i;
        sum += s;
        sum %= MOD;
    }
    cout << sum << endl;
    return 0;
}

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