/in/foo.cc: In function 'int main()':
/in/foo.cc:36:6: error: 'last' was not declared in this scope
      last[i][j]=i*N+j+1;
      ^~~~
/in/foo.cc:40:6: error: 'last' was not declared in this scope
      last[i][j]=(i+1)*N+j;
      ^~~~
/in/foo.cc:64:9: error: 'last' was not declared in this scope
      nx=last[x][y]/N;
         ^~~~