#include <bits/stdc++.h>
using namespace std;

int main() {
	freopen("branza.in", "r", stdin);
	freopen("branza.out", "w", stdout);
	int n, s, t;
	cin >> n >> s >> t;
	vector<vector<int>> v(n, vector<int>(2));
	for(int i = 0;i < n;++i)
		cin >> v[i][0] >> v[i][1];
	int start = 0;
	uint64_t ans = 0;
	
	while(start != -1)
	{
		int index = -1;
		for(int i = start;i <= min(n - 1, start + t);++i)
		{
			if(v[start][0] + s * (i - start) > v[i][0])
			{
				index = i;
				break;
			}
			ans += ((uint64_t) v[start][0] + s * (i - start)) * (uint64_t)v[i][1];
		}
		start = index;
	}
	cout << ans << "\n";
}