席一鸣 2014-10-15 03:30:50
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program aa;
var
sum,l,j,m,n,i:integer;
s1,s2:array[1..100]of integer;
a:array[0..10000]of boolean;
begin
readln(l,m);
sum:=0;
for i:=1 to m do
read(s1[i],s2[i]);
for i:=0 to l do
a[i]:=true;
for i:=1 to m do
for j:=s1[i] to s2[i] do
a[j]:=false;
for i:=0 to l do
if(a[i]) then
sum:=sum+1;
writeln(sum)
end.