Why do I get access violation? here's the code(top_sort with pointers)

type pok=^mars;
     mars=record
     redbr:integer;
     sleden:pok;
     end;
     var i,j,k,l,n,m,gl,r,pm,pm1:integer;
     brdeca,z,odg:array[1..100]of integer;
     p1,p2,p3,pom,prv:pok;
     toc:boolean;
     vl,kon,vl1:array[1..200]of integer;
     deca:array[1..150,1..150]of integer;
     t,tc,ozn:array[1..200]of boolean;
procedure stavi(y:integer);
begin
     if prv=nil then
     begin
          new(p1);
          prv:=p1;
          p1^.redbr:=y;
          p1^.sleden:=nil;
          kon[y]:=gl;
          gl:=gl+1;
     end else
     begin
          pom:=prv;
          while pom^.sleden<>nil do pom:=pom^.sleden;
          new(p2);
          pom^.sleden:=p2;
          p2^.sleden:=nil;
          p2^.redbr:=y;
          kon[y]:=gl;
          gl:=gl+1;
     end;
end;
procedure dfs(x:integer);
begin
      if tc[x]=false then
      begin
           tc[x]:=true;
           for j:=1 to brdeca[x] do vl[deca[x,j]]:=vl[deca[x,j]]+1;
           for j:=1 to brdeca[x] do if tc[deca[x,j]]=false then dfs(deca[x,j]);
      end;
end;
procedure vadi;
begin
          r:=prv^.redbr;
          for i:=1 to brdeca[prv^.redbr] do vl[deca[r,i]]:=vl[deca[r,i]]-1;
          pom:=prv;
          prv:=prv^.sleden;
          dispose(pom);
end;
begin
readln(n);
for i:=1 to n do ozn[i]:=false;
for i:=1 to n do vl[i]:=0;
for i:=1 to n do brdeca[i]:=1;
i:=1;
while i<n+1 do
begin
      read(deca[i,brdeca[i]]);
      if deca[i,brdeca[i]]<>0 then brdeca[i]:=brdeca[i]+1
      else
          begin
               brdeca[i]:=brdeca[i]-1;
               i:=i+1;
          end;
end;
gl:=0;
for i:=1 to n do
tc[i]:=false;
for i:=1 to n do dfs(i);
for i:=1 to n do vl1[i]:=vl[i];
toc:=true;
new(prv);
prv^.sleden:=nil;
for i:=1 to n do if vl[i]=0 then stavi(i);
while toc do
begin
     vadi;
     for i:=1 to brdeca[r] do if vl[deca[r,i]]=0 then stavi(deca[r,i]);
     if prv=nil then toc:=false;
end;
for i:=1 to n do z[i]:=i;
for i:=1 to n-1 do
begin
     for j:=i+1 to n do
     begin
          if kon[i]>kon[j] then
          begin
              pm:=z[i];
              pm1:=kon[i];
              z[i]:=z[j];
              kon[i]:=kon[j];
              z[j]:=pm;
              kon[j]:=pm1;
          end;
      end;
end;
for i:=1 to n-1 do write(z[i],' ');
write(z[n]);
end.