#include<bits/stdc++.h>
#define maxN 100005
using namespace std;
int n,s,t,i;
int cost[maxN],v[maxN],j;
long long sol[maxN],best;
inline int min(long long a,long long b)
{
    return a<b?a:b;
}
int main()
{
    freopen("branza.in","r",stdin);
    freopen("branza.out","w",stdout);
    scanf("%d%d%d",&n,&s,&t);
    for(int i=1;i<=n;i++)
    {
        scanf("%d%d",&cost[i],&v[i]);
        sol[i]=cost[i]*v[i];
    }
    i=1;
    for(int i=1;i<=n;i++)
    {
        for(int j=(i+1);j<=(i+t);j++)
            sol[j]=min(sol[j],1LL*(cost[i]*v[j]+s*(j-i)*v[j]));
    }
    for(int i=1;i<=n;i++)
    {
        best=best+sol[i];
    }
    printf("%lld\n",best);
    return 0;
}