var a:array[1..12] of longint;
        f,g:text;
        p,i,j,n:longint;

begin
a[1]:=25;
for i:=2 to 12 do
        a[i]:=5*a[i-1];
        assign(f,'fact.in');reset(f);
readln(f,p);
close(f);
n:=p*5;
i:=1;
while n>a[i] do
        inc(i);
dec(i);
for j:=1 to i do
        n:=n-5;
assign(g,'fact.out');rewrite(g);
writeln(n);
close(g);
end.