type vector=array [1..10000] of int64;
var j,o,i,p,d,c:longint;
    f,g:text;
    a,b:vector;
    l:real;
    r:int64;
function fact(x:longint):int64;
begin
o:=1;
for i:=1 to x do o:=o*i;
fact:=o;
end;
begin
assign(f,'fact.in');
reset(f);
assign(g,'fact.out');
rewrite(g);
read(f,p);
a[1]:=5;
b[1]:=1;
for i:=2 to p do        begin
                        a[i]:=a[i-1]*5;
                        b[i]:=b[i-1]*5+1;
                        end;
d:=p;
l:=0;
for j:=d downto 1 do begin
                     if p>=b[j] then    begin
                                        l:=l+(p/b[j])*j;
                                        p:=p mod b[j];
                                        end;
                     end;
c:=trunc(l)*5;
write(g,c);
close(f);
close(g);
end.