#include <stdio.h>
main()
{
int n,i,j,sign=1;
float fac,sum;
printf("please input value of n:");
scanf("%d",&n);
sum=0.0;
for(i=1;i<=2*n-1;i=i+2)
{
fac=1.0;
for(j=1;j<=2*i-1;j++)
{fac=fac*j;}
fac=fac*sign;
sum=sum+fac;
sign=-sign;
}
printf("sum=%.0f\n",sum);
getch();
}