#include<iostream> #include<cstdio> using namespace std; int main(){ int i,j,n,m,num = 0; int arr[10001]= {0}; int arr1[10001]={0}; scanf("%d %d",&n,&m); for(i = 0;i< m*2;i++) scanf("%d",&arr[i]); for(i = 0;i < m*2;i+=2){ for(j = arr[i];j <= arr[i+1];j++) arr1[j]= 1; } for(i = 0;i <= n;i++){ if(arr1[i] == 0)num++; } printf("%d\n",num); return 0; }