C++ :

#include <cstdio>
#include <cstring>
#include <algorithm>

using namespace std ;

struct Car {
    double cost ;
    bool cannot ;
    int left , right ;
    double V , has ;

    struct node {
        double v ;
        double money ;

        node( double v=0 , double money=0 ):v(v),money(money){}
        bool operator < ( const node a ) const {
            return money < a.money ;
        }

    }data[100000] ;



    Car( double V ):V(V){
        memset( data , 0 , sizeof( data ) ) ;
        cost = 0.0 ;
        cannot = false ;
        left = right = 0 ;
        has = 0.0 ;
    }

    void push( double t ) {
        if( cannot ) return ;
        node a(0,t) ;
        int p = lower_bound( data + left , data + right , a ) - data ;
        double c = 0.0 ;
        for( int i = p ; i < right ; i ++ ) c += data[i].v ;
        a.v = V - has + c ;
        data[p] = a ;
        right = p + 1 ;
        has = V ;
    }

    void use( double t ) {
        if( has < t || cannot ) {
            cannot = true ;
            return ;
        }
        has = has - t ;
        double c = 0.0 ;
        while( c + data[left].v < t ) {
            c += data[left].v ;
            cost += data[left].money*data[left].v ;
            left ++ ;
        }
        cost += data[left].money*(t-c) ;
        data[left].v -= t-c ;
    }

};


int main() {

    double S , V , D , P[10000] , dist[10000] ;
    int N ;
    scanf("%lf%lf%lf%lf%d" , &S , &V , &D , &P[0] , &N ) ;
    dist[0] = 0.0 ;
    for( int i = 1 ; i <= N ; i ++ ) {
        scanf("%lf%lf" , &dist[i] , &P[i] ) ;
    }

    Car ac( V ) ;
    ac.push( P[0] ) ;
    for( int i = 1 ; i <= N ; i ++ ) {
        ac.use( (dist[i]-dist[i-1])/D ) ;
        ac.push( P[i] ) ;
    }
    ac.use( (S-dist[N])/D ) ;
    if( ac.cannot ) printf("No Solution\n") ;
    else printf("%.2lf\n" , ac.cost ) ;

    return 0 ;
}