//#pragma GCC optimize("O3, Ofast, unroll-loops")
#include <bits/stdc++.h>
#define int long long
using namespace std;
struct Cows
{
    int c, p;
}v[100005];
signed main()
{
    ifstream cin("branza.in");
    ofstream cout("branza.out");
    int n, s, t, cnt=0, zero=0;
    cin>>n>>s>>t;
    for(int i=1; i<=n; i++)
    {
        cin>>v[i].c>>v[i].p;
    }
    for(int i=1; i<=n; i++)
    {
        int minn=1e9;
        for(int j=i-1; j>max(zero, i-1-t); j--)
        {
            if(v[j].p*(v[j].c+s*(j-i))<minn)
                minn=v[j].p*(v[j].c+s*(i-j));
        }
        cnt+=min(minn, v[i].p*v[i].c);
    }
    cout<<cnt;
    return 0;
}