CF425E Sereja and Sets

Let's assume that set $ S $ consists of $ m $ distinct intervals $ [l_{1},r_{1}] $ , $ [l_{2},r_{2}] $ , $ ... $ , $ [l_{m},r_{m}] $ ( $ 1

The first line contains integers $ n $ , $ k $ $ (1

In a single line, print the answer to the problem modulo $ 1000000007 $ $ (10^{9}+7) $ .