#include <iostream> using namespace std; int main() { int n, m,su = 0; cin >> n >> m; int a[n + 1] = {0}; int start,endd; for (int i = 1; i <= m; i++) { cin >> start >> endd; for (int j = start; j <= endd; j++) { a[j]++; } } for(int i=0;i<=n;i++){ if(a[i] == 0){ su++; } } cout << su; }