51nod 四级算法 4/74 P1051 最大子矩阵

uses math;
var
p,n,m,l,r,len:int64;
i,j,k:longint;
x,ans,y:int64;
f:array[0..500,0..500]of int64;
b:Array[0..500]of int64;
begin
readln(m,n);
for i:=1 to m do
begin
for j:=1 to n do
begin
read(f[i,j]);
end;

end;
ans:=0;
for i:=1 to m do
begin
fillchar(b,sizeof(b),0);
for j:=i to m do
begin
for k:=1 to n do
b[k]:=b[k]+f[j,k];
x:=0; y:=0;
for k:=1 to n do
begin
x:=x+b[k];
if x>=0 then y:=max(x,y)
else x:=0;
end;
ans:=max(ans,y);
end;
end;
writeln(ans);
end.