/in/foo.cc:8:5: error: conflicting declaration 'int n'
 int n, p, i, j, x, y, z, f;
     ^
/in/foo.cc:6:11: note: previous declaration as 'const int n'
 const int n = 201;
           ^
/in/foo.cc: In function 'void read()':
/in/foo.cc:12:22: warning: writing into constant object (argument 2) [-Wformat=]
  scanf("%d%d", &n, &p);
                      ^