program EmberAsh;
var
f:array[0..1000]of longint;
i,j,k,s,p,t1,t2,t3,t,s1,ss:longint;
fin,fout:text;

BEGIN
assign(fin,'goat.in');reset(fin);
assign(fout,'goat.out');rewrite(fout);
readln(fin,s,p);
f[0]:=0;
ss:=s;
for i:=1 to trunc(ss/3) do
  begin
  t1:=0;t2:=0;t3:=0;
  if f[i-1]-1>=0 then
    t1:=f[i-1]-1;
  if f[i-1]+2<=p then
    t2:=f[i-1]+2;
  if f[i-1]+5<=p then
    t3:=f[i-1]+5;
  if t1>t2 then
    begin
    t:=t1;
    s1:=1;
    end
      else
      begin
      t:=t2;
      s1:=5;
      end;
  if t<t3 then
    begin
    t:=t3;
    s1:=10;
    end;
  f[i]:=t;
  s:=s-s1;
  if s<=0 then
    begin
    writeln(fout,i);
    halt;
    close(fin);close(fout);
    end;
  end;
close(fin);close(fout);
END.