uses crt;
var a,b,c,d,n:longword;
begin
    clrscr;
    write('n=');readln(n);
    a:=1;b:=1;c:=1;d:=2;
    while c<n do
      begin
          d:=d+1;
          c:=a+b;
          a:=b;
          b:=c;
      end;
    write(n,' la phan tu thu ');
    if c=n then writeln(d,' trong day fibonacci')
      else writeln('0 trong day fibonacci');
readln;
end.

=================================

uses crt;
var n,i:longword;
    f:array[1..10000000] of longword;
begin
    clrscr;
    write('n=');readln(n);
    f[1]:=1;f[2]:=1;
    for i:=3 to n do f[i]:=f[i-1]+f[i-2];
    writeln('Phan tu thu ',n,' trong day fibonacci la ',f[n]);
readln;
end.

Nếu có sai thì nói mình nhé.

============================

program Hello;
uses crt;
var f:array[1..10000] of longint;
    i,n:longint;
begin
    clrscr;
    readln(n);
    f[1]:=1;
    f[2]:=1;
    for i:= 3 to n do
        f[i]:=f[i-1]+f[i-2];
    for i:= 1 to n do
        if n = f[i] then
            write('Vi tri: ', i);
end.

================================

program Hello;
uses crt;
var f:array[1..10000] of longint;
    i,n:longint;
begin
    clrscr;
    readln(n);
    f[1]:=1;
    f[2]:=1;
    for i:= 3 to n do
        f[i]:=f[i-1]+f[i-2];
    for i:= 1 to n do
        if n = i then
            write('Gia tri: ', f[i]);
end.