#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
constexpr ll INF = 4e18;
int X[100100], B[100100];
ll dp[100100];
struct Seg{
ll tree[300300];
int sz;
void init(int n){
sz = n;
fill(tree, tree+sz*2, -INF);
}
void update(int p, ll x){
p += sz;
tree[p] = max(tree[p], x);
for (p>>=1;p;p>>=1) tree[p] = max(tree[p<<1], tree[p<<1|1]);
}
ll query(int l, int r){
++r;
ll ret = -INF;
for (l+=sz, r+=sz;l<r;l>>=1, r>>=1){
if (l&1) ret = max(ret, tree[l++]);
if (r&1) ret = max(ret, tree[--r]);
}
return ret;
}
}tree;
int main(){
int _s, _e, k, A, n;
scanf("%d %d %d %d %d", &_s, &_e, &k, &A, &n);
X[0] = _s;
X[n+1] = _e;
for (int i=1;i<=n;i++){
scanf("%d %d", X+i, B+i);
}
vector<int> C;
for (int i=0;i<=n+1;i++){
C.push_back(X[i] % k);
}
sort(C.begin(), C.end());
C.erase(unique(C.begin(), C.end()), C.end());
tree.init(C.size() + 10);
int idx0 = lower_bound(C.begin(), C.end(), X[0] % k) - C.begin() + 1;
tree.update(idx0, (ll)(X[0]/k) * A);
for (int i=1;i<=n+1;i++){
dp[i] = -INF;
// naive
// for (int j=0;j<i;j++){
// if (X[i] % k > X[j] % k){
// dp[i] = max(dp[i], (dp[j] + (ll)(X[j]/k) * A) - ((ll)(X[i]/k) * A + A - B[i]));
// }
// else{
// dp[i] = max(dp[i], (dp[j] + (ll)(X[j]/k) * A) - ((ll)(X[i]/k) * A - B[i]));
// }
// }
int idx = lower_bound(C.begin(), C.end(), X[i] % k) - C.begin() + 1;
dp[i] = max(dp[i], tree.query(1, idx-1) - ((ll)(X[i]/k) * A + A - B[i]));
dp[i] = max(dp[i], tree.query(idx, (int)C.size()) - ((ll)(X[i]/k) * A - B[i]));
tree.update(idx, dp[i] + (ll)(X[i]/k) * A);
}
printf("%lld\n", dp[n+1]);
}
