#include<iostream> using namespace std; int main(){ int l,m,head,wei; cin>>l>>m; int a[l+1] ={0}; for(int i=1;i<=m;i++){ cin>>head>>wei; for(int j=head;j<=wei;j++){ a[j]++; } } int count = 0; for(int i=0;i<=l;i++){ if(a[i] == 0){ count++; } }cout<<count; }