#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;
    int i;
    for(i = 0; n > i; i++){
    	an = -2*an+4;
    }

    printf("数列a%dの値は%d\n", n, an);

	return 0;
}