Dijkstra O(n^2)

const
   sz = 5000;

var
   g:array[0..sz,0..sz] of longint;
   d:array[0..sz] of int64;
   used:array[0..sz] of boolean;
   i,j,n,m,u,min,s,e:longint;

procedure input;
var i,j:longint;
begin
  read(n,s,e);
  for i:=1 to n do
    for j:=1 to n do
      begin
        read(g[i][j]);
        if g[i][j] = -1 then
           g[i][j]:=maxlongint shr 1;
      end;
end;

procedure init;
var i:longint;
begin
  for i:=1 to n do
    if i <> s then
       d[i]:=maxlongint;
end;

procedure Dijkstra;
var i:longint;
begin
  for i:=1 to n do
    begin
      min:=maxlongint;
      for j:=1 to n do
        if (min > d[j]) and (not used[j]) then
           begin
             min:=d[j];
             u:=j;
           end;
      used[u]:=true;
      for j:=1 to n do
        if (d[j] > d[u] + g[u][j]) and (not used[j]) then
            d[j]:= d[u] + g[u][j];
    end;
end;

procedure answer;
begin
  if d[e] < maxlongint shr 1 then
     writeln(d[e])
  else
  writeln(-1);
end;

begin
  input;
  init;
  Dijkstra;
  answer;
end.