#include <stdio.h>
 
int rec(int n){
 
	int a,b,c;
	b=1;
	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;
	return 0;
}
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