View Compilation Error

0_0_11639573_32453.cpp: In function `void dfs(int, int, int)':
0_0_11639573_32453.cpp:20: error: `abs' undeclared (first use this function)
0_0_11639573_32453.cpp:20: error: (Each undeclared identifier is reported only once for each function it appears in.)
0_0_11639573_32453.cpp: In function `int main()':
0_0_11639573_32453.cpp:53: error: `abs' undeclared (first use this function)