program zx00;

var

a:array[1..10000] of boolean;

c,e,d,l,i,n,m:integer;

begin

read(n);

m:=n;

for i:=1 to n do

a[i]:=true;

readln(c);

for i:=1 to c do

begin

read(d,e);

readln;

for l:=d to e do

a[l]:=false;

end;

for i:=1 to n do

if a[i]=false then m:=m-1;

if m>3 then m:=m+1;

writeln(m);

end.