mrl_1994 2008-10-31 06:13:00
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program zxc5;
var
a,b,c:array[1..10000]of integer;
i,j,n,m,t,s,k,l:longint;
begin
readln(l,m);
for i:=1 to m do
readln(a[i],b[i]);
s:=0;
for i:=1 to m do
begin
c[i]:=b[i]-a[i]+1;
s:=s+c[i];
end;
k:=l-s;
write(k);
end.