hdu acm 第1592题哪里错了?代码如下,错误是 runtime error

hdu acm 第1592题哪里错了?代码如下,错误是 runtime error
Problem Description
Gardon bought many many chocolates from the A Chocolate Market (ACM).When he was on the way to meet Angel,he met Speakless by accident.
"Ah,so many delicious chocolates!I'll get half of them and a half!" Speakless said.
Gardon went on his way,but soon he met YZG1984 by accident.
"Ah,so many delicious chocolates!I'll get half of them and a half!" YZG1984 said.
Gardon went on his way,but soon he met Doramon by accident.
"Ah,so many delicious chocolates!I'll get half of them and a half!" Doramon said.
Gardon went on his way,but soon he met JGShining by accident.
"Ah,so many delicious chocolates!I'll get half of them and a half!" JGShining said.
.
.
.
After had had met N people ,Gardon finally met Angel.He gave her half of the rest and a half,then Gardon have none for himself.Could you tell how many chocolates did he bought from ACM?
Input
Input contains many test cases.
Each case have a integer N,represents the number of people Gardon met except Angel.N will never exceed 1000;
Output
For every N inputed,tell how many chocolates Gardon had at first.
Sample Input
2
Sample Output
7
题目分析可知是2的（n+1）次方减去1；
#include
int f[1001][1001];
void add(int k)
{
int i;
for(i=0;i