简单的数论题目zju1652（不知道有没有AC，因为我在zju上没帐号）PKU上没有

代码是在新校区机房写的，关键是找出递归公式！

/*
Count the Regions

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Time limit: 1 Seconds Memory limit: 32768K
Total Submit: 318 Accepted Submit: 207

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What's the maximum number of regions definable by N zig-zag lines, each of which consists of two parallel infinite half-lines joined by a straight line segment?

Here is an example of 2 zig-zag lines yield 12 regions at the most.

Input

The input consists of a sequence of N (<= 10000), which is the number of the zig-zag lines, one per line.

Output

For each N, you should output the number of the maximum regions.

Sample Input

1
2
Sample Output

2
12

*/
#include "stdio.h"
#include "vector"

using namespace std;

int main()
{
int n,i,j;
vector<int> p;
scanf("%d",&n);
if(n<0||n>10000)
return 0;
p.push_back(2);
for(i=1;i<n;i++){
j=p.back()+9*i+1;
p.pop_back();
p.push_back(j);
}
j=p.back();
printf("%d/n",j);
return 0;
}