OMM 2000 Problem 2

A triangle of numbers is constructed as follows. The first row consists of the numbers from $1$ to $2000$ in increasing order, and under any two consecutive numbers their sum is written. (See the example corresponding to $5$ instead of $2000$ below.) What is the number in the lowermost row?

1 2 3 4 5 3 5 7 9 8 12 16 20 28 4