TJU 2346 Gauß in Elementary School Solution

Problem Statement :
Difficulty : Easy.
Problem Type : Mathematics,Gauss Sum.

Johann Carl Friedrich Gauß(1777-1855) was one of the most important German mathematicians . For those of you who remember the Deutsche Mark, a picture of him was printed on the 10,-DM bill. In elementary school, his teacher J. G. Buttner tried to occupy the pupils by making them add up the integers from 1 to 100. The young Gauß surprised everybody by producing the correct answers (5050) within seconds. Can you write a computer program that can compute such sums really quickly?

Problem

Given two integers n and m, you should compute the sum of all the integers from n to m.

Here is the C implementation of the solution.

#include <stdio.h>

int main(){
 long long low,up;
 int n,i,j;
 scanf("%d",&n);
 for(i = 1;i <= n;i++){
  scanf("%lld %lld",&low,&up);
  printf("Scenario #%d:\n%lld\n\n",i,((low+up)*(up-low+1))/2);
 }
 return 0;
}