#include <bits/stdc++.h>
using namespace std;
int main() {
int n, m;
cin >> n >> m;
vector<bool> trees(n + 1, 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 <= n; i++) {
if (trees[i]) {
count++;
}
}
cout << count << endl;
return 0;
}
