#include <fstream>
#include <queue>

using namespace std;

ifstream f("branza.in");
ofstream g("branza.out");

const int nmax = 1005;
int n, s, t, p[nmax], c[nmax];
long long dp[nmax];
deque<int> q;

int main()
{
    f >> n >> s >> t;
    for(int i = 1; i <= n; i ++)
        f >> c[i] >> p[i];

    for(int i = 1; i <= n; i ++)
    {
        while(!q.empty() && q.front() < i - t)
            q.pop_front();

        while(!q.empty() && c[i] <= c[q.back()] + s * (i - q.back()))
            q.pop_back();

        q.push_back(i);
        dp[i] = c[q.front()] + s * (i - q.front());
    }

    long long sumi = 0;
    for(int i = 1; i <= n; i ++)
        sumi += dp[i] * p[i];

    g << sumi;
    return 0;
}