#include <bits/stdc++.h>
#define int long long
#define ld long double
using namespace std;

ld dis , a , b , c , ans = 1145141919810.114514;
int n;
ld d[51] , p[51];

void dfs(int dep , ld dist , ld res)
{
	if(dist < d[dep]) return;
	if(dep > n) return;
	if(dist >= dis)
	{
		ans = min(res,ans);
		return;
	}
	ld lft = (dist-d[dep])/b;
	dfs(dep+1,dist,res);
	if(lft*2 < a) dfs(dep+1,d[dep]+a*b,res+20+(a-lft)*p[dep]);
}

signed main()
{
	ios::sync_with_stdio(false);
	cin.tie(0);
	cin >> dis >> a >> b >> c >> n;
	for(int i = 1; i <= n ; ++i)
	{
		cin >> d[i] >> p[i];
	}
	dfs(1,a*b,c);
	cout << ans;
	return 0;
}