View Compilation Error

0_0_8194764_7814.cpp: In function `double dfs(int, int, int, int, int)':
0_0_8194764_7814.cpp:18: error: `abs' undeclared (first use this function)
0_0_8194764_7814.cpp:18: error: (Each undeclared identifier is reported only once for each function it appears in.)