标签：ios iostream turn ret stream clu include ace using
#include <iostream>
using namespace std;
int main() {
double n;
cin>>n;
long long sum = 0;
sum = (1+n)*n/2;
cout<<sum;
return 0;
}标签：ios iostream turn ret stream clu include ace using
原文地址：https://www.cnblogs.com/ZCWang/p/12158829.html
