monitor dp
{
   enum {thinking, hungry, eating} state[5];
   condition self[5];

   void pickup(int i) {
      state[i] = hungry;
      if ((state[(i+4)%5] != eating) && (state[(i+1)%5] != eating)) {
         state[i] = eating;
      else
         self[i].wait();
   }

   void putdown(int i) {
      state[i] = thinking;
      if ((state[(i+4)%5] == hungry) && (state[(i+3)%5] != eating)) {
          state[(i+4)%5] = eating;
          self[(i+4)%5].signal(); 
      }
      if ((state[(i+1)%5] == hungry) && (state[(i+2)%5] != eating)) {
          state[(i+1)%5] = eating;
          self[(i+1)%5].signal(); 
      }
   }

   void init() {
      for (int i = 0; i < 5; i++)
         state[i] = thinking;
   }
}