#include <stdio.h>
#define N 100000

int dq[N], v[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++;
    int st = 0, dr = -1;
    long long suma = 0;
    for (int i = 0; i < n; i++)
    {
        int c;
        fscanf(in, "%d%d", &v[i], &c);
        if (st <= dr && dq[st] == i - k)
        {
            st++;///eliminam branza stricata
        }
        while (st <= dr && v[i] <= v[dq[dr]] + s * (i - dq[dr]))
        {
            dr--;
        }
        dq[++dr] = i;
        suma += (long long)c * (v[dq[st]] + s * (i - dq[st]));
    }
    fprintf(out, "%lld\n", suma);
    fclose(in);
    fclose(out);
    return 0;
}