#include<bits/stdc++.h>
using namespace std;
double km;
double l,a,money;
int n;
double km2[51],single[51];
int main(){
	//1、声明变量，输入
	cin>>km;
	cin>>l>>a>>money>>n;
	double sx=a*l,my=a*l,yl=l,ml=l;
	for(int i=1;i<=n;i++){
		cin>>km2[i]>>single[i];
	}
	km2[n+1]=km;
	//2、计算过程
	for(int i=1;i<=n;i++){
		sx-=(km2[i]-km2[i-1]);
		yl-=(km2[i]-km2[i-1])/a;
		if(km2[i+1]-km2[i]>sx || yl<ml/2){
			money+=20;
			money+=(ml-yl)*single[i];
			yl=ml;
			sx=my;
		}
	}
	//3、输出
	cout<<fixed<<setprecision(1)<<money+0.05;
	return 0;
}
/**
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 X   X       J      Q     Q
  X X        J     Q       Q
   X         J     Q       Q
  X	X        J      Q   Q  Q
 X	 X     J J       Q Q Q
X	  X     JJ            Q Q
*/