program wells_ska;

uses sysutils, strutils;

var
  M, N: integer;
  A: array of array of integer;
  B: array of array of double;
  i, j, ki, kj: integer;
  t, u, u1, u2: double;
  rezt: double;

label
  to_rezt;

begin
 //assign(input, 'input.txt'); reset(input);
 //assign(output, 'output.txt'); rewrite(output);
 readln(M, N);
 setLength(A, M+1, N+1);
 setLength(B, M+1, N+1);

 for i := 1 to M do
   for j := 1 to N do begin
     read(a[i, j]);
     b[i, j] := 0;
   end;

 for i := 1 to M do
   for j := 1 to N do begin
     for ki := -1 to 1 do
       for kj := -1 to 1 do begin
         if (i+ki < 1) or (i+ki >M) or (j+kj < 1) or (j+kj > N) then
           continue;
         if (ki=0) and (kj=0) then
           t := 1
         else
           t := 0.5;
         b[i, j] := b[i, j] + t * a[i+ki, j+kj];
       end;
 end;

 u1 := b[1, 1];
 for i := 1 to M do
   for j := 1 to N do
     if u1 < b[i, j] then
        u1 := b[i, j];

  u2 := -1;
  for i := 1 to M do
   for j := 1 to N do begin
     if b[i, j] < u1 then
       continue;
     u := -1;
     for ki := 1 to M do
       for kj := 1 to N do begin
         if (abs(i-ki) < 3) and (abs(j-kj) < 3) then
           continue;
         if b[ki, kj] > u then
           u := b[ki, kj];
       end;
     if u > u2 then begin
       u2 := u;
       if u2=u1 then
         goto to_rezt;
     end;
   end;

to_rezt:

 rezt := u1+u2;

 writeln(rezt:0:1);
 close(input);
 close(output);

end.