#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; }