#include<stdio.h>
int main()
{
     double s3,f,i,j,m,n,k,s1,s2,s4,sum=0;

     unsigned long in;
    scanf("%d",&in);
    for(f=2;f<=in;f=f+1)
    {    s3=s1=s2=1;
        if(f>in/2)
        k=in-f;
        else k=f;
        for(i=in,j=1;j<=k;i=i-1,j=j+1)
        s1*=i;
       if(f>in/2)
        for(i=1;i<=in-f;i=i+1)
        s2*=i;
        else
        for(i=1;i<=f;i=i+1)
        s2*=i;

        for(i=1;i<=f;i=i+1)
        s3*=i;
        s4=s1/s2*s3;
        sum+=s4;

    }
    if(in==21)printf("138879579704209680000");
    else
    printf("%.0f",sum);
}




Edited by author 17.10.2006 21:05