1911번

1911

#include <iostream>
#include <vector>
#include <algorithm>

using namespace std;

bool compare(pair<int, int> a, pair<int, int> b) {
	return a.first < b.first;
}

int main() {
	int n, l;
	vector<pair<int, int> > v;
	cin >> n >> l;
	for (int i = 0; i < n; i++) {
		int start, end;
		cin >> start >> end;
		v.push_back(make_pair(start, end - 1));
	}

	sort(v.begin(), v.end(), compare);
	

	int tmpStart = -1;
	int cnt = 0;
	for (int i = 0; i < n; i++) {
		int start = v[i].first;
		int end = v[i].second;
		
		if(tmpStart < start) {
			tmpStart = start;
		}
		
		while(tmpStart <= end) {
			tmpStart += l;
			cnt++;
			
		}
	}
	cout << cnt;
}