package main
import (
	"fmt"
)
func main() {
	var d,s,ans int
	tree := make([]bool,10000)
	fmt.Scanf("%d %d",&d,&s)
	for i:=0;i<d;i++{
		tree[i] = true;
	}
	for i:=0;i<s;i++{
		var t1,t2 int
		fmt.Scanf("%d %d",&t1,&t2)
		for j:=t1;j<=t2;j++{
			if tree[j] {tree[j] = false}
		}
	}
	for i:=0;i<=d+2;i++{
		if tree[i] {ans++}
	}
	fmt.Print(ans);
}

为什么样例过后是297而不是298/kk