Program P1;
var n,m,s,nr : qword;
    fi,fo : text;
begin
      assign(fi,'fact.in'); reset(fi); readln(fi,nr); close(fi);
      assign(fo,'fact.out'); rewrite(fo);
      s:=0; n:=2*nr+2;
      if (nr<=9) and (nr>4) then n:=4*nr-1
      else if (nr>10) and (nr<10000000) then n:=4*nr+4
                                        else if nr>900000000 then n:=nr*4+14;
      if n>2 then begin while s<>nr do begin
                                       m:=5; s:=0; n:=n+1;
                                       while m<=n do begin
                                                      s:=s+ (n div m) ;
                                                      m:=m*5;
                                                      end;
                                       end;
                        writeln(fo,n);
                   end

              else writeln(fo,'1');
       close(fo);
end.