program ex;

var

l,m,i,j:longint;

a,b:array[1..100] of longint;

BEGIN

read(l,m);

for i:= 1 to m do

read(a[i],b[i]);

inc(l);

for i:= 1 to m do

for j:= a[i] to b[i] do

dec(l);

writeln(l);

END.