program number;
var
m,n:integer;
data,f:array[0..11,0..11]of integer;
ans:integer;

procedure init;
var
i,j:integer;
begin
assign(input,'number.in');
reset(input);
assign(output,'number.out');
rewrite(output);
readln(m,n);
for i:=1 to m do
 begin
 for j:=1 to n do read(data[i,j]);
 readln;
 end;
close(input);
ans:=-1;
end;

procedure main;
var
i,j,t:integer;
begin
 for i:=1 to m do
  for j:=1 to n do
  begin
  f[i,j]:=data[i,j];
  if i=1 then f[i,j]:=data[i,j]+f[i,j-1];
  if j=1 then f[i,j]:=data[i,j]+f[i-1,j];
  if f[i,j-1]<=f[i-1,j] then t:=f[i,j-1]
   else t:=f[i-1,j];
  f[i,j]:=f[i,j]+t;
  end;
end;

begin
init;
main;
if f[m,n]>0 then
writeln(f[m,n])
else writeln(ans);
close(output);
end.