500 3
150 300
100 200
470 471
#include<iostream>
#include<iomanip>
using namespace std;
bool a[10001]={0};
int main(){
int b,l,d,m;
int e=0;
a[10001]=1;
cin>>l>>m;
for (int i=0;i<l;++i) a[i]=1;
for (int j=0;j<m;++j){
cin>>b>>d;
for(int i=b;i<d;++i) a[i]=0;
}
for (int i=1;i<l;++i){
if (a[i]) e++;
}
cout<<e;
return 0;
}