View Compilation Error

0_0_29194420_20532.cpp: In function 'int main(int, char**)':
0_0_29194420_20532.cpp:58:10: error: 'M' was not declared in this scope
   if (st/M==0 || st%M==0 || st/M==H-1 || st%M==W-1) {
          ^