#include <iostream>
#define MAX 100
#define min(a,b) (a)<(b)?(a):(b)

using namespace std;

double Distance,MaxL,Cost;
double V[MAX],F[MAX],S[MAX];
int N;

void init()
{
	int i;
	freopen("tour.in","r",stdin);
	freopen("tour.out","w",stdout);
	cin >> Distance >> MaxL >> Cost >> F[0] >> N;
	for (i=1;i<=N;i++)
		cin >> S[i] >> V[i];
}


void solve()
{
	int i,k;
	double Dis;
	for (i=1;i<=N;i++)
	{
		F[i]=0x7FFFFFF;
		for (k=0;k<=i-1;k++)
		{
			Dis=(S[i]-S[k]) / Cost;
			if (Dis >= MaxL / 2 && Dis <= MaxL)
				F[i]=min(F[i],F[k]+ Dis * V[i] +20);
		}
	}
	F[N+1]=0x7FFFFFF;
	for (k=1;k<=N;k++)
	{
		Dis=(Distance-S[k]) / Cost;
		if (Dis <= MaxL)
			F[N+1]=min(F[N+1],F[k]+ Dis * V[k]);
	}
	printf("%.1lf",F[N]);
}

int main()
{
	init();
	solve();
	return 0;
}