#include <stdio.h>

int main(){
    int a,i,j,ans=0,bufa=1,bufb=1;
    scanf("%d",&a);
    for(i=1;i<=a/2;i++){
        for(j=0;j<a-2*i;j++)bufa*=(a-i-j);
        for(j=a-2*i;j>0;j--)bufb*=j;
        ans+=bufa/bufb;
    }    
    printf("%d\n",ans+1);
}