//Hey, welcome to HDOJ(Hangzhou Dianzi University Online Judge). //In this problem, your task is to calculate SUM(n) = 1 + 2 + 3 + ... + n. #include<stdio.h> int main() {     int N, n, i;     while(scanf("%d", &n)!=EOF)     {         N=0;         for(i=1; i<=n; i++)            N=N+i;         printf("%d\n\n", N);     }     return 0; }