#include <iostream> using namespace std; int main() { int L,M; cin>>L>>M; bool trees[10001]; for (int i=0;i<=L;i++) { trees[i]=true; } for (int i=0;i<M;i++) { int start,end; cin >>start>>end; for (int j=start;j<=end;j++) { trees[j]=false; } } int count=0; for (int i=0;i<=L;i++) { if (trees[i]) { count++; } } cout<<count<<endl; return 0; }