SPOJ-ESYRCRTN Why Always Recursion

SPOJ-ESYRCRTN

$F(1)=1 \\ F(2)=3\\F(N)=F(N-1)-F(N-2),给出n,求\sum_{i=1}^n F[i]$

推前几项可以知道，和是循环的

#include <cstdio>
using namespace std;
int ls[]={1,4,6,5,2,0};
int main()
{
    int T;
    long long n;
    for(scanf("%d",&T);T--;)
    {
        scanf("%lld",&n);
        printf("%d\n",ls[(n-1)%6]);
    }
    return 0;
}