#include<bits/stdc++.h>
using namespace std;
typedef long long ll;
template<class T> bool maximize(T &a, const T &b){ return (a < b ? a = b, 1 : 0); }
template<class T> bool minimize(T &a, const T &b){ return (a > b ? a = b, 1 : 0); }
#define fi first
#define se second
#define pb push_back
#define ii pair<int, int>
#define all(x) x.begin(), x.end()
#define TASK "nonsense"
/// end of template ///
const int N = 1e5 + 10;
int k,m,d,a,n,t[N],b[N];
ll dp[N];
namespace sub1
{
bool check()
{
return (n<=1000);
}
const ll inf = 3e18;
void solve()
{
t[0]=k,b[0]=0;
t[n+1]=m,b[n+1]=0;
for(int i=1;i<=n+1;++i)
{
dp[i]=-inf;
for(int j=0;j<i;++j) maximize(dp[i],-((t[i]-t[j]+d-1)/d*1LL*a)+dp[j]+b[i]);
// cout<<i<<' '<<dp[i]<<'\n';
}
cout<<dp[n+1];
}
}
void solve()
{
cin>>k>>m>>d>>a>>n;
for(int i=1;i<=n;++i) cin>>t[i]>>b[i];
if(sub1::check()) return void(sub1::solve());
}
int main() {
ios_base::sync_with_stdio(0);
cin.tie(0);
cout.tie(0);
// freopen(TASK".inp","r",stdin);
// freopen(TASK".out","w",stdout);
int testcase=1;
// cin>>testcase;
while (testcase--)
solve();
return 0;
}
