#include<bits/stdc++.h>
#define maxN 100005
using namespace std;
int n,s,t,m[maxN],v[maxN],c[maxN],l,st,dr;
int q[2*maxN+5];
long long sol;
int main()
{
    freopen("branza.in","r",stdin);
    freopen("branza.out","w",stdout);
    scanf("%d%d%d",&n,&s,&t);
    for(int i=1;i<=n;i++)
    {
        scanf("%d%d",&c[i],&v[i]);
    }
    m[1]=c[1];
    st=1;
    dr=1;
    q[st]=1;
    l=t;
    for(int i=2;i<=n;i++)
    {
        while(st<=dr && q[st]<=(i-l)) st++;
        while(st<=dr && ((m[q[dr]]+s*(i-q[dr]))>=c[i])) dr--;
        if(st<=dr) m[i]=m[q[st]]+s*(i-q[st]);
            else
        {
            m[i]=c[i];
            q[++dr]=i;
        }
    }
    for(int i=1;i<=n;i++)
    {
        sol=sol+1LL*m[i]*v[i];
    }
    printf("%lld\n",sol);
    return 0;
}