🚀 go-pugleaf

One may use the following observations: all zeros come from 5's and 2's, and
there are more 2's than 5's.

Now, since last digit of product depend solely upon the last digits
of the  multipliers, we keep only the last digits. We also collect
all 2's separately, ahhihilating them with 5's, when possible.


var LastDigit, Count, 
    Multiplier, Twos : integer;

const Stop = 1000;

begin
  LastDigit:=1; 
  Twos:=0;
  for Count:=1 to Stop do begin
    While (Multiplier mod 2) = 0 do begin
      Twos:=Twos+1;
      Multiplier:=Multiplier div 2;
    end;
    While (Multiplier mod 5) = 0 do begin
      Twos:=Twos-1;
      Multiplier:=Multiplier div 5;
    end;
    LastDigit:=(LastDigit*Multiplier) mod 10;
  end;
  for Count:=1 to Twos do 
    LastDigit:=(LastDigit*2) mod 10;
end.





--
Zhenya Sorokin

E-mail     : sorokin@ps1.iaee.tuwien.ac.at, sor@rs6.iaee.tuwien.ac.at
Paper-mail : E. Sorokin, Gusshausstr. 27/359-4, 1040 Vienna, Austria
Voice-mail : +43(1)58801-3703, -3948
Fax-mail   : +43(1)504 2477