View Compilation Error

0_0_30646822_7636.cpp: In function 'bool spfa()':
0_0_30646822_7636.cpp:49:26: error: 'm' was not declared in this scope
      if(++cn[v] > sqrt(n+m)) return true; // 存在正环
                          ^
0_0_30646822_7636.cpp:49:27: error: 'sqrt' was not declared in this scope
      if(++cn[v] > sqrt(n+m)) return true; // 存在正环
                           ^