program huaxue;

var a,f:array[-1..500,-1..500] of longint;

i,m,n,l,maxn:longint;

function max(ii,ll:longint):longint;

begin

if ii>ll then exit(ii) else exit(ll);

end;

procedure work(x,y:longint);

var j,k:longint;

begin

f[x,y]:=1;

for j:=-1 to 1 do

for k:=-1 to 1 do

begin

if ((j+k=-1) or (j+k=1)) and (a[x+j,y+k]f[x,y]) then f[x,y]:=f[x+j,y+k]+1;

end;

end;

end;

begin

fillchar(f,sizeof(f),-1);

read(m,n);

for i:=1 to m do

for l:=1 to n do

begin

read(a);

f:=0;

end;

for i:=1 to m do

for l:=1 to n do

begin

work(i,l);

if f>maxn then maxn:=f;

end;

writeln(maxn);

end.