Program fact;
 var p,i,f,j,n:longint;
     a:array[1..100] of int64;
     fi,fo:textfile;
 begin
 assign(fi,'fact.in');reset(fi);
 assign(fo,'fact.out');rewrite(fo);
 read(fi,p);
 if p=0 then writeln(fo,1) else
 begin
 n:=0;f:=0;a[1]:=5;
  while f<p do
   begin
   inc(n);
   f:=0;
   for i:=1 to n do
         if i mod 5=0 then begin
               inc(f);
              for j:=1 to 12 do begin
                               a[j+1]:=a[j]*5;
                               if i=a[j] then f:=f+j-1;
                               end;
                     end;
                     if f>p then n:=-1;
       end;
    writeln(fo,n);
    end;
 close(fi);
 close(fo);
 end.