#include<bits/stdc++.h> using namespace std; int main () { int l,m,i,s[10001]={},s1[10001]={},sum=0; cin>>l>>m; for(i=0;i<m*2;i++){ cin>>s1[i]; } for(i=0;i<m*2;i+=2){ for(int j=s1[i];j<=s1[i+1];j++){ s[j]=1; } }for(i=0;i<=l;i++){ if(s[i]==0){ sum++; } } cout<<sum<<endl; return 0; }