#include<iostream>
using namespace std;
int main()
{
unsigned long i,j,count=0; //unsigned long : 0-4,294,967,295
cin>>j;
for(i=0;i<=j;i++)
{
count=count+i;
}
cout<<count<<endl;
cin.get();
return 0;
}原文：https://www.cnblogs.com/l574/p/14983617.html