#include <stdio.h>

int main()
{
	int l,m;
	scanf("%d %d",&l,&m);
	int a[10000]={0};
	int tree[1000]={1};
	int i;
	for(i=0;i<=l;i++){
		tree[i]=1;
	} 
	for(i=0;i<m*2;i++){
		scanf("%d",&a[i]);
	}
	int j;
	for(i=0;i<m*2;i+=2){
		for(j=a[i];j<=a[i+1];j++){
			if(tree[j]==1){
				tree[j]=0;
			}
		}
	}
	int sum = 0;
	for(i=0;i<=l;i++){
		sum=sum+tree[i];	
	}
	printf("%d",sum);
	return 0;
 }