UVA 10079

http://uva.onlinejudge.org/index.php?option=com_onlinejudge&Itemid=8&category=24&page=show_problem&problem=1020

切披萨的问题，写出前十个数，推出通项公式1+n*(n+1)/2，即可解答

#include<stdio.h>
int main()
{
 long long n;
 while(scanf("%lld",&n)&&n>=0)
      printf("%lld\n",1+n*(n+1)/2);    return 0;
}