var n,i,s: integer;
begin
readln(n);
s:=0;
for i:=1 to n do
if i mod 5=0 then s:=s+i;
writeln(s);
end.
var n,i,s: integer;
begin
readln(n);
s:=0;
for i:=1 to n do
if i mod 5=0 then s:=s+i;
writeln(s);
end.