program factorial;
var f,g:text;                               {1 cifra de 0... 1*2*3*4*5}
    i,p,gasit,nr,i1:longint;                {4 cifre de 0 ... 5*..10*..15..20}
begin
     assign(f,'fact.in');
     assign(g,'fact.out');
     reset(f);
     rewrite(g);
     read(f,p);
     gasit:=0;
     i:=0;
     if p>=99999999 then
     begin
          i:=400000010;
          gasit:=99999999;
     end else
       if p>=49999999 then
       begin
            i:=200000005;
            gasit:=49999999;
       end else
         if p>=9999999 then
         begin
              i:=40000005;
              gasit:=9999999;
         end else
           if p>=4999999 then
           begin
                i:=20000000;
                gasit:=4999999;
           end else
             if p>=999999 then
             begin
                  i:=4000000;
                  gasit:=999999;
             end else
              if p>=499999 then
              begin
                   i:=2000000;
                   gasit:=499999;
              end else
                 if p>=99999 then
                 begin
                      i:=400000;
                      gasit:=99999;
                 end else
              if p>=49999 then
              begin
                   i:=200005;
                   gasit:=49999;
              end else
                     if p>=9999 then
                     begin
                          i:=40005;
                          gasit:=9999;
                     end else
                         if p>=999 then
                         begin
                              i:=4000;
                              gasit:=999;
                         end else
                             if p>=99 then
                             begin
                                  i:=400;
                                  gasit:=99;
                             end;

     while(gasit<p) do
     begin
          i:=i+5;
          i1:=i;
          {cautam toti divizorii de 5,
          adica de cate ori se imparte la 5 produsul nostru,
          mergem din 5 in 5 cu cautarea 5,10, 15.....}
          while (i1 mod 1953125=0) do
          begin
               i1:=i1 div 1953125;
               gasit:=gasit+9;
          end;



          while (i1 mod 390625=0) do
          begin
               i1:=i1 div 390625;
               gasit:=gasit+8;
          end;


          while (i1 mod 78125=0) do
          begin
               i1:=i1 div 78125;
               gasit:=gasit+7;
          end;

          while (i1 mod 15625=0) do
          begin
               i1:=i1 div 15625;
               gasit:=gasit+6;
          end;


          while (i1 mod 3125=0) do
          begin
               i1:=i1 div 3125;
               gasit:=gasit+5;
          end;

          while (i1 mod 625=0) do
          begin
               i1:=i1 div 625;
               gasit:=gasit+4;
          end;

          while (i1 mod 125=0) do
          begin
               i1:=i1 div 125;
               gasit:=gasit+3;
          end;
          while (i1 mod 5=0) do
          begin
               i1:=i1 div 5;
               gasit:=gasit+1;
          end;
     end;
     if p=0 then nr:=1
            else nr:=i;
     write(g,nr);
     close(f);
     closE(g);
end.