代码如下：

#include <bits/stdc++.h>
using namespace std;
int x,y,f[10001],n,l,ans;
int main() {
	cin>>n>>l;
   // memset (f,0,sizeof (f));
    for (int i=1;i<=n;i++) {
    	cin>>x>>y;
    	for (int j=x;j<=y;j++) 
    	  f[j]=1;
	}
	for (int i=0;i<=10000;i++)
       if (f[i]==0) ans++;
    cout<<ans;
  	return 0;
}