#include <stdio.h>
//a{n} = -6a{n-1} -9a{n-2}, a{1}=1, a{2}=2(再帰なし版)

int main(void) {
    int n = 4;
    int a, b = 2, c = 1; 
    for(int i = 3; i <= n; i++){
        a = -6*b -9*c;
        c = b;
        b = a;
    }
    printf("数列a%dの値は%d\n", n, a);
	return 0;
}