#include <iostream>
#include <algorithm>
#include <vector>
using namespace std;
int main()
{
int l,m;
cin>>l>>m;
l++;
int nums[l];
fill(nums,nums+l,1);//初始化数组为1
while(m--)
{
int u,v;
cin>>u>>v;
int count =0;
for(int i=u;i<=v;i++)
{
if(nums[i] != 0)
{
nums[i] = 0;
}
count++;
}
}
int count=0;
for(int i=0; i<=l; i++)
{
if(nums[i] == 1)
{
count++;
}
}
cout<<count;
}