CF450B Jzzhu and Sequences

Jzzhu has invented a kind of sequences, they meet the following property: You are given $ x $ and $ y $ , please calculate $ f_{n} $ modulo $ 1000000007 $ $ (10^{9}+7) $ .

The first line contains two integers $ x $ and $ y $ $ (|x|,|y|

Output a single integer representing $ f_{n} $ modulo $ 1000000007 $ $ (10^{9}+7) $ .

In the first sample, $ f_{2}=f_{1}+f_{3} $ , $ 3=2+f_{3} $ , $ f_{3}=1 $ . In the second sample, $ f_{2}=-1 $ ; $ -1 $ modulo $ (10^{9}+7) $ equals $ (10^{9}+6) $ .