#include <bits/stdc++.h>
using namespace std;
#define endl '\n'
#define ll long long
const ll Tid=-1e18;
ll TT(ll le,ll ri){
return max(le,ri);
}
struct segtree{
vector<ll> seg;
vector<int> coor;
int n,lg;
void refresh(int v){
seg[v]=TT(seg[v<<1],seg[(v<<1)|1]);
}
void build(vector<int> &a){
coor=a;
sort(coor.begin(),coor.end());
coor.erase(unique(coor.begin(),coor.end()),coor.end());
n=1;
while(n<coor.size()){
n<<=1;
}
lg=__lg(n);
seg.assign(n<<1,Tid);
}
int getidx(int x){
return (lower_bound(coor.begin(),coor.end(),x)-coor.begin());
}
void update(int l,ll x){
l=getidx(l);
l+=n;
seg[l]=max(seg[l],x);
for(int i=1;i<=lg;i++){
refresh(l>>i);
}
}
ll query(int l,int r){
l=getidx(l),r=getidx(r);
if(l>=r){
return Tid;
}
l+=n,r+=n;
ll curr=Tid;
for(;l<r;l>>=1,r>>=1){
if(l&1){
curr=TT(curr,seg[l]);
l++;
}
if(r&1){
r--;
curr=TT(curr,seg[r]);
}
}
return curr;
}
};
signed main(){
if(fopen("input.txt","r")){
freopen("input.txt","r",stdin);
}
ios_base::sync_with_stdio(false);
cin.tie(NULL);
int k,m,d,a,n;
cin >> k >> m >> d >> a >> n;
a=-a;
vector<int> x;
x.push_back(k);
vector<int> coor;
coor.push_back(k%d);
int b[n+1];
for(int i=1;i<=n;i++){
int t;
cin >> t >> b[i];
coor.push_back(t%d);
x.push_back(t);
}
coor.push_back(m%d);
for(int i=0;i<coor.size();i++){
if(coor[i]==0){
coor[i]+=d;
}
}
x.push_back(m);
b[0]=0,b[n+1]=0;
ll DP[n+2];
DP[0]=0;
segtree seg;
seg.build(coor);
seg.update(d,0-(1LL*a*((x[0]+d-1)/d)));
for(int i=1;i<=n+1;i++){
//cout << "PHASE " << i << endl;
int temp=x[i]%d;
if(temp==0){
temp+=d;
}
DP[i]=Tid;
DP[i]=max(DP[i],seg.query(1,temp)+1LL*a*((x[i]+d-1)/d)+a);
DP[i]=max(DP[i],seg.query(temp,d+1)+1LL*a*((x[i]+d-1)/d));
//cout << i << ' ' << DP[i] << endl;
DP[i]+=b[i];
seg.update(temp,DP[i]-1LL*a*((x[i]+d-1)/d));
//cout << "ANS " << DP[i] << endl;
}
cout << DP[n+1];
}
