import java.math.BigDecimal;

public class Test
{
    
    public static BigDecimal calcSum(BigDecimal[] arr, int num)
    {
        if (num <= 0 || num > arr.length)
        {
            return null;
        }
        BigDecimal big = new BigDecimal(0);
        for (int i = 0; i < num; i++)
        {
            big = big.add(arr[i]);
        }
        return big;
    }
    
    public static void main(String[] args)
    {
        MyArr myArr = new MyArr(1000);
        System.out.println(calcSum(myArr.getArr(), 1000));
    }
}


class MyArr
{
    private BigDecimal[] arr;
    
    public BigDecimal[] getArr()
    {
        return this.arr;
    }
    
    public MyArr(int length)
    {
        if (length < 2 || length > 1000)
        {
            return;
        }
        arr = new BigDecimal[length];
        arr[0] = new BigDecimal(1);
        arr[1] = new BigDecimal(2);
        for (int i = 2; i < length; i++)
        {
            arr[i] = arr[i-1].add(arr[i-2]);
        }
    }
}