백준 1292

백준 1292

#include<iostream>
#include<vector>
using namespace std;

int main()
{
	vector<int> v;
	int cnt=0;
	int val = 1;
	while (cnt < 1000)
	{
		for (int i = val; i > 0; i--)
		{
			v.push_back(val);
			cnt++;
		}
		val++;
	}
	int a, b,result=0;
	cin >> a >> b;
	for (int i = a - 1; b > i; i++)
		result+=v[i];
	cout << result;
}