hdu 5066 Harry And Physical Teacher(物理题 弹性碰撞)

#include <algorithm>#include <cstring>#include <cstdio>#include <iostream>using namespace std;long long  v1 , v2;int main ( ){    while ( ~scanf ( "%lld%lld" , &v1 , &v2 ) )    {        printf ( "%lld\n" , 2*v1 - v2 );    }}