type atype=set of 0..10001;

arrest=array[1..100] of atype;

var a:arrest;

b:array[1] of atype;

i,j,l,m,x,y:longint;

begin

read(l,m);

for i:=1 to 100 do a[i]:=[];

for i:=1 to m do

begin

read(x,y);

a[i]:=[x..y];

end;

b[1]:=[10001];

for i:=1 to m do

b[1]:=b[1]+a[i];

j:=l+1;

for i:=0 to 10000 do

if i in b[1] then dec(j);

writeln(j);

end.