#include "stdio.h"int main(){	int fib[42],fibsum[42];	int i,n;	fib[1]=fib[2]=1;	fibsum[1]=1;	fibsum[2]=2;	for(i=3;i<=41;i++){		fib[i]=fib[i-1]+fib[i-2];		fibsum[i]=fibsum[i-1]+fib[i];	}	scanf("%d",&n);	printf("%d",fibsum[n]);	return 0;}