wangtao37 2019-07-22 02:51:42
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var
n,q,i,j,x,y,s:longint;
a:array[0..10000] of boolean;
begin
readln(n,q);
for i:=1 to q do
begin
readln(x,y);
for j:=x to y do a[j]:=true;
end;
for i:=0 to n do if a[i] then inc(s);
writeln(n-s+1);
end.