program cojs1682;
var
  v:array[0..1010]of boolean;
  a:array[1..10000010]of longint;
  i,k,l,r,n,m,ans:longint;

begin
assign(input,'ha14d.in');reset(input);
assign(output,'ha14d.out');rewrite(output);

  readln(n,m);
  for k:=1 to m do
  begin
    readln(l,r);
    for i:=l to r do
      a[i]:=k;
  end;
  fillchar(v,sizeof(v),0);
  for i:=1 to n do
    v[a[i]]:=true;
  for i:=1 to m do
    if v[i] then inc(ans);
  writeln(ans);

close(input);close(output);
end.