[白俊2513]スクールバス

#include <bits/stdc++.h>	

const int dx[4] = { 1,0,-1,0 };
const int dy[4] = { 0,-1,0,1 };

using namespace std;
	
int n, k, s;
pair<int, int > p[30001];
priority_queue<pair<int, int>, vector<pair<int, int>>, greater<pair<int, int>>> pq;

int main() {
	cin.tie(0); cout.tie(0); ios_base::sync_with_stdio(false);
	cin >> n >> k >> s;
	for (int i = 0; i < n; i++) {
		cin >> p[i].first >> p[i].second;
	}
	p[n] = { s,0 };
	sort(p, p + n + 1);
	int T = lower_bound(p, p + n + 1, make_pair(s, 0)) - p;
	for (int i = 0; i < T; i++) pq.push({ p[i].first - s, p[i].second });

	int ans = 0;
	int t = k;
	int c = 0;
	while (!pq.empty()) {
		if(t == k)
			c += abs(pq.top().first);
		if (pq.top().second <= t) {
			t -= pq.top().second;
			pq.pop();
			if (t == 0) {
				ans += 2 * c;
				t = k;
				c = 0;
			}
		}
		else {
			auto temp = pq.top();
			temp.second -= t;
			t = k;
			pq.pop();
			pq.push(temp);
		}
	}
	ans += 2 * c;

	priority_queue<pair<int, int>> Q;
	for (int i = T + 1; i <= n; i++) Q.push({ p[i].first - s, p[i].second });
	t = k;
	c = 0;
	while (!Q.empty()) {
		if (t == k)
			c += abs(Q.top().first);
		if (Q.top().second <= t) {
			t -= Q.top().second;
			Q.pop();
			if (t == 0) {
				ans += 2 * c;
				t = k;
				c = 0;
			}
		}
		else {
			auto temp = Q.top();
			temp.second -= t;
			t = k;
			Q.pop();
			Q.push(temp);
		}
	}
	ans += 2 * c;

	cout << ans;
	return 0;
}