#include <fstream>
#include <stdlib.h>
#include <iostream>
using namespace std;

ifstream in ("gutui.in");
ofstream out("gutui.out");

int n, h, u, r = 0, nr = 0;

struct gutuie {
	int h;  // inaltimea la care se  afla initial
	int g;  // greutatea
    int nc; // nr max de gutui culese dupa care devine inaccesibila
            // numit "nivel"
};

gutuie *gutui;
/*
int fcmp(const void* fp1, const void* fp2) {
	fruct* f1 = (fruct*)fp1;
	fruct* f2 = (fruct*)fp2;
	float r1 = f1->g / f1->h,
	      r2 = f2->g / f2->h;
	return r1 - r2 < 0 ? -1 : 1;
}

int fcmp1(const void* fp1, const void* fp2) {
	fruct* f1 = (fruct*)fp1;
	fruct* f2 = (fruct*)fp2;
	return f2->g - f1->g;
}
*/

int cmp_h(const void* fp1, const void* fp2) {
	gutuie* f1 = (gutuie*)fp1;
	gutuie* f2 = (gutuie*)fp2;
	return f2->h - f1->h;
}

int cmp_g(const void* fp1, const void* fp2) {
	gutuie* f1 = (gutuie*)fp1;
	gutuie* f2 = (gutuie*)fp2;
	return f1->g - f2->g;
}

void print() {
     for (int i = 0; i < n; i++) {
         printf("%d %d %d\n", gutui[i].h, gutui[i].g, gutui[i].nc);
     }
     printf("\n");
}


int main() {
    
	in >> n >> h >> u;
	gutui = new gutuie[n];
	for (int i = 0; i < n; i++) {
		in >> gutui[i].h >> gutui[i].g;
		gutui[i].nc = (h - gutui[i].h) / u;
		r  += gutui[i].g;
		nr += gutui[i].nc;
    }
    qsort(gutui, n, sizeof(gutuie), cmp_g);	
    --n;
    int i = 0, limit = n*(n+1) / 2;
    while (nr < limit) {
          r -= gutui[i].g;
          --n;
          limit = n*(n+1) / 2;
          nr -= gutui[i++].nc;
    }
    out << r;
	return 0;
}