#include<cstdio>
#include<deque>
using namespace std;
struct Week{
    int c,p;
};
const int N=100000;
Week v[N+1];
deque<int>d;
int n,s,t;
long long sum;
void scan(){
    int i;
    scanf("%d%d%d",&n,&s,&t);
    for(i=1;i<=n;i++)
        scanf("%d%d",&v[i].c,&v[i].p);
}
void init(){
    freopen("branza.in","r",stdin);
    freopen("branza.out","w",stdout);
    scan();
}
void solve(){
    int i;
    for(i=1;i<=n;i++){
        while(!d.empty()&&v[i].c<=v[d.back()].c+(i-d.back())*s)
            d.pop_back();
        d.push_back(i);
        if(i-d.front()==t+1)
            d.pop_front();
        sum+=(v[d.front()].c+(i-d.front())*s)*v[i].p;
    }
}
int main(){
    init();
    solve();
    printf("%lld",sum);
    return 0;
}