#include <algorithm>
#include <cstdio>
#include <iostream>
#include <utility>

using namespace std;

double d1;
double c;
double d2;
int n;
pair<double, double> num[11];
double res;

int main () {
    
    freopen ("lyuxing.in", "r", stdin);
    freopen ("lyuxing.out", "w", stdout);
    
    cin >> d1 >> c >> d2 >> num[0].second >> n;
    num[n + 1].first = d1;
    for (int i = 1; i <= n; i++) {
        cin >> num[i].first >> num[i].second;
    }
    sort (num + 1, num + n + 1);
    
    int i = 0;
    double oil = 0;
    while (true) {
        if (i == n + 1) {
            break;
        }
        
        for (int j = i + 1; j <= n + 1; j++) {
            if (num[j].second < num[i].second) {
               if ((num[j].first - num[i].first) / d2 < c) {
                   res += ((num[j].first - num[i].first) / d2 - oil) * num[i].second;
                   oil = 0;
                   i = j;
                   goto end;
               }
            }
        }
        
        if (num[i + 1].first - num[i].first > c * d2) {
            cout << "No Solution" << endl;
            return 0;
        }
        
        res += (c - oil) * num[i].second;
        oil = c;
        for (int j = i + 1; j <= n + 1; j++) {
            if (num[j].first - num[i].first <= oil * d2) {
                oil -= (num[j].first - num[i].first) / d2;
                i = j;
            }
            else {
                break;
            }
        }
        
        end:;
    }
    
    printf ("%.2lf", res);
    
    return 0;
}