#include <fstream>
#include <deque>

using namespace std;

ifstream f("branza.in");
ofstream g("branza.out");

int n,s,t,i,c[100002],kg[100002],marime,ultimul,p,u;

long long suma;

//deque <int> d;
int d[100002];

int main()
{
    f>>n>>s>>t;
    for(i=1;i<=n;i++)
    {
        f>>c[i]>>kg[i];
    }
    //d.push_back(1);
    //suma+=c[1]*kg[1];
    p=1;
    u=0;
    for(i=1;i<=n;i++)
    {
        //marime=d.size();
        //ultimul=d.back();
        while(p<=u && c[d[u]]+(i-d[u])*s > c[i])
        {
            u--;
        }
        d[++u]=i;
        if(i-d[p]==t+1)
            ++p;
        suma+=1LL*(c[d[p]]+(i-d[p])*s)*kg[i];
    }
    g<<suma;
    return 0;
}