This is my "var"

const
  big=3000;
var
  i,j,k,l,m,n,l1,l2,now,sum,res,last:longint;
  f:array[1..big,1..2000]of integer;
  ans:array[1..2500]of longint;
  a:array[1..2000]of record
                       x1,y1,x2,y2,col:longint;
                     end;
  x:array[1..2,0..2000]of longint;
  mi:array[1..2,0..10000]of longint;

I think I only use about 12MB memory,but the system told me that I got MLE on test 1.
Why?Why?