int a[N][N];

  int Water( void ) {
    int x,y,s=0,flag;
    do {
      flag = 0;
      for( y=1; y<N-1; y++ ) {
        for( x=1; x<N-1; x++ ) {
          int c = a[x][y];
          int d = Min( Min(a[y+0][x-1],a[y+0][x+1]), Min(a[y-1][x+0],a[y+1][x+0]) );
          if( c<d ) a[x][y]=d, s+=d-c, flag=1;
        }
      }
    } while( flag );
    return s;
  }