#include<stdio.h>
int func(int n){
	int a;
	int b=1;
	int c=2;
	for(int i=3;i<=n;i++){
		a=-2*c+2*b;
		b=c;
		c=a;
	}
	return a;
}

int main (void){
	int n=3;
	printf("%d",func(n));
	return 0;
}