#include <fstream>

using namespace std;
int v[100001];
int d[100001];
ifstream cin("branza.in");
ofstream cout("branza.out");
int main(){
    int n,k,i,sum=0,s,t,a;
    cin>>n>>s>>t;
    int st=0,dr=-1;
    for(i=1; i<=n; i++){
        cin>>v[i];cin>>a;
        if(d[st]==i-t){st++;}
        while(st<=dr&&v[i]<=(v[d[dr]]+(i-d[dr])*s))dr--;
        d[++dr]=i;
        sum+=a*(v[d[st]]+(i-d[st])*s);}
    cout<<sum;return 0;}