#include <fstream>

using namespace std;

ifstream cin("branza.in");
ofstream cout("branza.out");

long long v[100001],dq[100001];

int main()
{
    long long n,i,s,t,st=1,dr=0,nrr;
    long long p=0,s2,s1;
    cin>>n>>s>>t;
    for(i=1; i<=n; i++)
    {
        cin>>v[i]>>nrr;
        while(dr>=st && v[i]<=v[dq[dr]]+(i - dq[dr]) * s)
            dr--;
        dr++;
        dq[dr]=i;
        if(dq[st]+t<i)
            st++;
        //s2=v[i]*nrr;
        //p=v[dq[st]]*nrr;
        p+=v[dq[st]]*nrr + s*(i-dq[st])*nrr;
        //p += min(s1,s2);
    }
    cout<<p;
    return 0;

}