10分钟一次性AC

#include<iostream>
using namespace std;
int sum(int l, int r)
{
    int sum=0;
    for(int i=l;i<=r;i++)
        sum+=i; 
    return sum;
}
int main()
{
    //freopen("xxx.in","r",stdin);
    //freopen("yyy.out","w",stdout);
    int l,r;
    cin >> l >> r;
    cout << sum(l,r);
    //fclose(stdin);
    //fclose(stdout);
    return 0;
}