/DEMSO0 - Đếm số không bên phải

              USES CRT;
        var    n,m,k,res,temp1,temp2,temp3,temp4:int64;
        r1,r2:extended;
        s1,s2,s3,st:ansistring;
        i,j,l:longint;
        a,b,dem1:array[-5000000..5000000] of int64;
        dem2:array['A'..'z'] of int64;

        begin
            readln(n);
            i:=5; res:=0;
            while i<=n do begin
                j:=i;
                while j mod 5=0 do begin
                    inc(res);
                    j:=j div 5;
                end;
                inc(i,5);
            end;
            writeln(res);
            //readln;
        end.