#include <bits/stdc++.h>
using namespace std;
const int N = 1e5+15;
#define ll long long
ll tree[N*4];
void update_ind(int pos,int l,int r,int ind,ll upd){
if(l==r){
tree[pos]= upd;
return;
}
int mid = (l+r)/2;
if(ind<=mid)
update_ind(pos*2,l,mid,ind,upd);
else
update_ind(pos*2+1,mid+1,r,ind,upd);
tree[pos]= max(tree[pos*2],tree[pos*2+1]);
}
ll query(int pos,int l,int r,int ql,int qr){
if(r<ql || qr<l)return -4e18;
if(ql<=l && r<=qr)return tree[pos];
int mid = (l+r)/2;
return max(query(pos*2,l,mid,ql,qr),query(pos*2+1,mid+1,r,ql,qr));
}
int x[N],b[N];
map<int,int> Hash;
int main(){
//freopen("input.txt","r",stdin);
int k,m,d,a,n;
scanf("%d%d%d%d%d",&k,&m,&d,&a,&n);
x[0]= k;
x[n+1]= m;
for(int i=1;i<=n;++i)scanf("%d%d",&x[i],&b[i]);
for(int i=0;i<N*4;++i)tree[i]= -4e18;
for(int i=0;i<=n+1;++i){
int u = x[i]%d;
Hash[u];
}
int pos=0;
for(map<int,int>::iterator it= Hash.begin();it!=Hash.end();++it){
it->second = pos++;
}
ll q;
ll xx,val;
int id;
for(int i=0;i<=n+1;++i){
xx = x[i]/d;
val = -a*xx;
xx = x[i]%d;
id = Hash[xx];
if(i==0){
q = 0;
}
else{
q = -4e18;
if(id>0)
q= query(1,0,pos-1,0,id-1) -a;
q = max(q,query(1,0,pos-1,id,pos-1));
q+= val;
q+=b[i];
}
update_ind(1,0,pos-1,id, q-val);
}
cout<<q<<endl;
}
