#include<cstdio>
#include<deque>
using namespace std;
int main()
{
    freopen("branza.in","r",stdin);freopen("branza.out","w",stdout);
    deque<int>d;int n,s,t,v1[100005],v2[100005],i,pr=0;
    scanf("%d%d%d",&n,&s,&t);
    for(i=1;i<=n;++i)
    {
        scanf("%d%d",&v1[i],&v2[i]);
        while(!d.empty()&&(i-d.back())*s>v1[i]-v1[d.back()])
            d.pop_back();
        d.push_back(i);
        if(i-t==d.front())
            d.pop_front();
        if(i==d.front())
            pr+=v2[i]*v1[d.front()];
        else
            pr+=v2[i]*v1[d.front()]+v2[i]*s*(i-d.front());
    }
    printf("%d",pr);
}