#include <iostream> using namespace std; int main(){ int n,lines,s,f,cnt=1; cin>>n>>lines; int len[n]={}; for (int i=1;i<=lines;i++){ cin>>s>>f; for (int i=s-1;i<f;i++){ len[i]=1; } } for (int i=0;i<n;i++){ if(len[i]==0){ cnt++; } } cout<<cnt; return 0; }