时间超时，需要增进速度


#include 
#include 
using namespace std;
long long a, b, c, k, a1[5] = {};
int main()
{
    cin >> a >> b >> c >> k;
    for (long long i = 1; i <= k; i++)
    {
        a1[1] = b + c;
        a1[2] = a + c;
        a1[3] = a + b;
        a = a1[1];
        b = a1[2];
        c = a1[3];
    }
    if (abs(a - b) < 1000000000000000000)
        cout << a - b << endl;
    else
        cout << "unfair" << endl;
    return 0;
}

有没有人帮忙提下速？
就是这一部分


```c++
for (long long i = 1; i <= k; i++)
    {
        a1[1] = b + c;
        a1[2] = a + c;
        a1[3] = a + b;
        a = a1[1];
        b = a1[2];
        c = a1[3];
    }

```

你这循环里都没有用到i，这是在循环啥呢