#include <stdio.h>
#define NMAX 100100

int Q[NMAX], val[NMAX];

int main()
{
	int N, S, T, p = 1, u = 0, C, P;
	long long sol = 0;
	
	freopen("branza.in", "r", stdin);
	freopen("branza.out", "w", stdout);
	
	scanf("%d%d%d", &N, &S, &T);
	for (i = 1; i <= N; i++)
	{
		scanf("%d%d", &C, &P);
		
		val[i] = C - i * S;
		while (p <= u && val[i] <= val[Q[u]])
			u--;
		Q[++ u] = i;
		
		sol += (long long)P * (val[Q[p]] + i * S);
		
		if (Q[p] + T == i)
			p ++;
	}
	
	printf ("%lld", sol);
	return 0;
}