#include<iostream> #include<cmath> #include<cstdio> using namespace std; int main() //主函数入口 { 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; //结束整个程序 }