时间限制：C/C++/Rust/Pascal 1秒，其他语言2秒
空间限制：C/C++/Rust/Pascal 256 M，其他语言512 M
64bit IO Format: %lld
空间限制：C/C++/Rust/Pascal 256 M，其他语言512 M
64bit IO Format: %lld
题目描述
YZ is the king of the kingdom. There are n cities in his kingdom. To celebrate the 50th anniversary of the founding of his country, YZ decided to distribute supplies as a reward to all the cities.
We all know that the further the city is from the capital (always at 1), the more it will cost to transport. We define K as the shortest distance between a city and the capital, and ignore the difference in distance between different cities(all is 1 unit). Cost from capital to the city is
.
We all know that the further the city is from the capital (always at 1), the more it will cost to transport. We define K as the shortest distance between a city and the capital, and ignore the difference in distance between different cities(all is 1 unit). Cost from capital to the city is
Now YZ gives you the map of his kingdom, and asks you if you can calculate the total cost.
(We guarantee that it is a connected graph.)
输入描述:
The first line contains two integers n and m, which means there are n cities and m roads.
The next m lines contains two integers u and v, denoting there is a road connecting city u and city v.
输出描述:
Print the only line containing a single integer. It should be equal to the total cost mod 1e9+7.