#include<bits/stdc++.h>
#define mare 1e9
#define mod 1000000007
#define bit(x,i)(((x)>>(i))&1)
#define FAST ios_base::sync_with_stdio(false); cin.tie(NULL); cout.tie(NULL);
using namespace std;
ifstream fin("branza.in");
ofstream fout("branza.out");
long long int T,n,m,ok,x,y,i,j;
long long int c,aux,start,maxx,summax,minn;
long long int s,dr,mij,contor,suma,poz;
long long int v[100005];
deque<long long int> q;
int main()
{
    fin>>n>>s>>T;
    for(i=1;i<=n;i++)
    {
        fin>>x>>y;
        v[i]=x;
        while(!q.empty() && v[i]<=v[q.back()]+s*(i-q.back()))
            q.pop_back();
        q.push_back(i);
        while(!q.empty() && i-q.front()>T)
            q.pop_front();
        contor=contor+y*(v[q.front()]+s*(i-q.front()));
    }
    fout<<contor;
    return 0;
}