#include <fstream>

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