#include <stdio.h>
#include <stdlib.h>
#define N 100000

int cost[N], dq[N];

int main()
{
    FILE *in, *out;
    in = fopen("branza.in", "r");
    out = fopen("branza.out", "w");
    int n, s, k;
    fscanf(in, "%d%d%d", &n, &s, &k);
    k++;
    long long sum = 0;
    int st = 0, dr = -1;
    for (int i = 0; i < n; i++)
    {
        int cantitate;
        fscanf(in, "%d%d", &cost[i], &cantitate);
        ///cat timp dq e e nevid si v[i] e mai bun sau egal cu cel mai prost din dq
        while (st <= dr && cost[i] <= cost[dq[dr]] + (i - dq[dr]) * s)
        {
            dr--;///elimin din dreapta
        }
        if (st <= dr && dq[st] == i - k)
        {
            st++;///elimin din stanga
        }
        dq[++dr] = i;
        sum += (long long)cantitate * (cost[dq[st]] + (i - dq[st]) * s);
    }
    fprintf(out, "%lld\n", sum);
    fclose(in);
    fclose(out);
    return 0;
}