#include <iostream> #include <vector> using namespace std; int main() { int L, M; cin >> L >> M; vector<bool> removed(L + 1, false); for (int i = 0; i < M; i++) { int start, end; cin >> start >> end; for (int j = start; j <= end; j++) { removed[j] = true; } } int remainingTrees = 0; for (int i = 0; i <= L; i++) { if (!removed[i]) { remainingTrees++; } } cout << remainingTrees << endl; return 0; }