POJ-2084-Game of Connections

#include<cstdio>
#include<cstring>
#include<iostream>
#define Mod 10000
using namespace std;
int ans[1201],len;
void GetAns(int n)
{
len=1;
ans[0]=1;
for(int i=2*n;i>2*n-n;i--)
{
int res=0;
for(int j=0;j<len;j++)
{
ans[j]=ans[j]*i+res;
res=ans[j]/Mod;
ans[j]%=Mod;
}
if(res)
ans[len++]=res;
}
for(int i=2;i<=n+1;i++)
{
int res=0;
for(int j=len-1;j>=0;j--)
{
ans[j]+=res*Mod;
res=ans[j]%i;
ans[j]/=i;
}
while(!ans[len-1])
len--;
}
}
int main()
{
int n;
while(scanf("%d",&n)&&n!=-1)
{
GetAns(n);
printf("%d",ans[len-1]);
for(int i=len-2;i>=0;i--)
printf("%04d",ans[i]);
printf("\n");
}
return 0;
}