#include <stdio.h>
//a{n+1} = -2a{n} + 4, a{0}=2(再帰なし版)
int main(void) {
    int n = 4;
    int an = 2;
	for(int i = 0;i<n;i++){
		an = -2*an + 4;
	}
    printf("数列a%dの値は%d\n", n, an);

	return 0;
}