#include <stdio.h>
//練習問題G
 
int func(int n){
    int a, b=2, c=1;
    int i;
    for(i=0;i<n;i++){
    	a=c;
    	c=b;
    	b=-2*c+2*a;
    }
    return a;
}
int main(void) {
	int n = 3;
    printf("数列anについて, n=%dのときの値は%d\n", n
, func
(n
)); 	return 0;
}
 
				I2luY2x1ZGUgPHN0ZGlvLmg+Ci8v57e057+S5ZWP6aGMRwogCmludCBmdW5jKGludCBuKXsKICAgIGludCBhLCBiPTIsIGM9MTsKICAgIGludCBpOwogICAgZm9yKGk9MDtpPG47aSsrKXsKICAgIAlhPWM7CiAgICAJYz1iOwogICAgCWI9LTIqYysyKmE7CiAgICB9CiAgICByZXR1cm4gYTsKfQppbnQgbWFpbih2b2lkKSB7CglpbnQgbiA9IDM7CiAgICBwcmludGYoIuaVsOWIl2Fu44Gr44Gk44GE44GmLCBuPSVk44Gu44Go44GN44Gu5YCk44GvJWRcbiIsIG4sIGZ1bmMobikpOwoJcmV0dXJuIDA7Cn0K