#include<fstream>
using namespace std;
ifstream in("branza.in");
ofstream out("branza.out");
const int N = 100005;
long long v[N],p[N],n,s,t,dq[N],st=1,dr,r;
void stanga(int i){
    if(i-dq[st]>t) st++;
}
void dreapta(int i){
    while(dr>=st && v[i]<=(v[dq[dr]])+(i-dq[dr])*s) dr--;
}
int main(){
    int i;
    in>>n>>s>>t;
    for(i=1;i<=n;i++) in>>v[i]>>p[i];
    for(i=1;i<=n;i++){
        if(i>=t) stanga(i);
        dreapta(i);
        dq[++dr]=i;
        r+=(v[dq[st]]+(i-dq[st])*s)*p[i];
    }
    out<<r;
    return 0;
}