Don't use maxint, you have overflow here, I think:
a[i,k]+a[k,j]
In 32-bit compilers integer = longint, so maxint = 2147483647, like Delphi.

You can use something like this:
const
...inf = 1000000;
..........
for i:=1 to n do
...for j:=1 to n do
......a[i,j]:=inf;