#include <bits/stdc++.h>
#define pb push_back

using namespace std;

ifstream fin("branza.in");
ofstream fout("branza.out");

void debug_out() { cerr << '\n'; }
template <typename Head, typename... Tail> void debug_out(Head H, Tail... T) { cerr << " " << H; debug_out(T...);}
#define dbg(...) cerr << #__VA_ARGS__ << " ->", debug_out(__VA_ARGS__)
#define dbg_v(x, n) do{cerr<<#x"[]: ";for(int _=0;_<n;++_)cerr<<x[_]<<" ";cerr<<'\n';}while(0)
#define dbg_ok cerr<<"OK!\n"

typedef pair<int,int> pii;
typedef long long int ll;
typedef long double ld;

const int DMAX = 1e5+10;

deque <pii> dq;

int n,s,t;
ll ans;

int main(){
    ios_base::sync_with_stdio(false);
    cin.tie(0);

    int i;
    ll x,y;

    fin>>n>>s>>t;
    for(i=1;i<=n;i++){
        fin>>x>>y;
        if(!dq.empty() && dq.front().first+t < i)
            dq.pop_front();
        while(!dq.empty() && dq.back().second + (i-dq.back().first)*s >= x)
            dq.pop_back();
        dq.pb({i,x});
        ans+=1LL*((i-dq.front().first)*s+dq.front().second)*y;
    }
    fout<<ans<<'\n';

    return 0;
}