const fi = '';
fo = '';
var n, i: longint;
procedure Stop;
begin
close(input); close(output);
halt;
end;
begin
assign(input, fi); reset(input);
assign(output, fo); rewrite(output);
readln(n);
for i:=n div 5 downto 0 do
if (n-5*i) mod 3 = 0 then
begin
writeln(i + (n-5*i) div 3);
Stop;
end;
writeln(-1);
close(input); close(output);
end.
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