求菲波拉契数列第n项的值

public int Solution(int n)
{
    if(n < 3)
    {
        return 1;
    }else
    {
        int[] arr = new int[n];
        arr[0] = 1;
        arr[1] = 1;
        for(int i = 3;i <= n;i++)
        {
            arr[i] = arr[i-1] + arr[i-2];
        }
        return arr[n];
    }
}