program factorial;   
  
{$APPTYPE CONSOLE}  
  
uses
  SysUtils;

Label IESIRE;
var fin,fout:text;   
    f,min,div2,div5,i,j,p,n:integer;   
    ok:boolean;   
{*----------MAIN--------*}
begin  
        assign(fin,'fact.in');
        assign(fout,'fact.out');   
        reset(fin);
        rewrite(fout);   
        readln(fin,p);
        if p = 0 then begin writeln(fout,1); goto IESIRE end;

        div2:=p;
        div5:=p;
        i:=0;
        while ((div2 >0) or (div5>0)) do
        begin
                inc(i);
                f:=i;
                while ((f mod 2 = 0) and (div2 > 0)) do
                begin
                        dec(div2);
                        f:=f div 2;
                end;

                while ((f mod 5 = 0) and (div5 > 0)) do
                begin
                        dec(div5);
                        f:=f div 5;
                end;

        end;
        writeln(fout,i);
        //if ok then writeln(fout,n) else writeln(fout,-1);
        IESIRE:
        close(fout);
end.