#include <stdio.h>
#include <stdlib.h>

#define maxn 55
#define inf 999999

const double eat=20.0;

typedef struct Jiayou{
	double pos;
	double pri;
}Jiayou;

int n;
double goal,full,far,kml,ans,f[maxn];
Jiayou jia[maxn];
FILE *f1,*f2;

inline double min(double a,double b)
{
	return a<b?a:b;
}

int cmp(const void *a,const void *b)
{
	return (((Jiayou*)a)->pos > ((Jiayou*)b)->pos?1:-1);
}

void dp(int x)
{
	int i,j;
	double pos,pri,zan;
	pos=jia[x].pos;
	pri=jia[x].pri;
	if (goal-pos<=far)
	{
		f[x]=0;
		return;
	}
	for (i=n;i>x;i--)
	{
		if (jia[i].pos-pos<=far)
		{
			zan=eat+(jia[i].pos-pos)/kml*jia[i].pri;
			if (f[i]==inf)
				dp(i);
			f[x]=min(f[x],f[i]+zan);
			break;
		}
	}
	for (j=i-1;j>x;j--)
	{
		if (jia[j].pos-pos>far/2)
		{
			zan=eat+(jia[j].pos-pos)/kml*jia[j].pri;
			if (f[j]==inf)
				dp(j);
			f[x]=min(f[x],f[j]+zan);
		}
		else
			break;
	}
}

void run(void)
{
	dp(0);
	ans+=f[0];
}

void ini(void)
{
	int i;
	fscanf(f1,"%lf",&goal);
	fscanf(f1,"%lf%lf%lf",&full,&kml,&ans);
	fscanf(f1,"%d",&n);
	for (i=1;i<=n;i++)
		fscanf(f1,"%lf%lf",&jia[i].pos,&jia[i].pri);
	qsort(jia,n+1,sizeof(jia[0]),cmp);
	far=kml*full;
	for (i=0;i<=n;i++)
		f[i]=inf;
}

int main(void)
{
	f1=fopen("tour.in","r");
	f2=fopen("tour.out","w");
	ini();
	run();
	fprintf(f2,"%.1lf",ans);
	fclose(f1);fclose(f2);
	return 0;
}