const max=5200;
var zs:array[1..max]of longint;
    sz:array[1..max]of longint;
    num,n,m,out:longint;
procedure add(k:longint);
var t:longint;
begin
     for t:=1 to num do
         begin
              if k mod zs[t]=0 then
                 begin
                      k:=k div zs[t];
                      inc(sz[t]);
                 end;
              if k=1 then
                 break;
         end;
end;
procedure minus(k:longint);
var t:longint;
begin
     for t:=1 to num do
         begin
         if k mod zs[t]=0 then
            begin
                 k:=k div zs[t];
                 dec(sz[t]);
            end;
         if k=1 then
            break;
         end;
end;
procedure init;
var t,k:longint;
    q:boolean;
begin
     num:=0;
     fillchar(zs,sizeof(zs),0);
     fillchar(sz,sizeof(sz),0);
     readln(n,m);
     for t:=2 to 50000 do
         begin
              q:=true;
              for k:=2 to trunc(sqrt(t)) do
                  if t mod k=0 then
                     begin
                          q:=false;
                          break;
                     end;
              if q then
                 begin
                      inc(num);
                      zs[num]:=t;
                 end;
         end;
     for t:=n downto m+1 do
         add(t);
     for t:=2 to n-m do
         minus(t);
end;
procedure make;
var t:integer;
begin
     out:=0;
     for t:=1 to num do
         if sz[t]>0 then
            inc(out);
end;
procedure print;
begin
     writeln(out);
end;
begin
     init;
     make;
     print;
end.