Program P1;
var n,s,nr,i : longint;
    fi,fo : text;
    a:array[1..20] of int64;

begin assign(fi,'fact.in'); reset(fi); readln(fi,nr); close(fi);
      a[1]:=5; for i:=2 to 20 do a[i]:=5*a[i-1];
      assign(fo,'fact.out'); rewrite(fo);
      if nr<2 then write(fo,'1') else begin s:=0; n:=2*nr+2;
      while s<>nr  do begin
                      i:=1;
                      s:=0;
                      n:=n+1;
                      while a[i]<=n do begin
                                       s:=s+(n div a[i]);
                                       i:=i+1;
                                       end;
                      end;
                      end;
      write(fo,n);
      close(fo);
end.