#include <cstdio>
#include <set>
using namespace std;
const int maxn = 100005;
multiset <int> diff;
int C[maxn];
int P[maxn];
int main()
{
    freopen("branza.in", "r", stdin);
    freopen("branza.out", "w", stdout);
    int n, S, t;
    scanf("%d%d%d", &n, &S, &t);
    for(int i = 1; i <= n; i++)
        scanf("%d%d", &C[i], &P[i]);
    unsigned long long ans = 0;
    for(int i = 1; i <= n; i++)
    {
        diff.insert(C[i] - i * S);
        if(i > t)
            diff.erase(C[i - t] - (i - t) * S);
        int aux = *diff.begin();
        ans = ans + 1LL * P[i] * (i * S + aux);
    }
    printf("%lld\n", ans);
    return 0;
}