#include <iostream>
#include <vector>
 
using namespace std;
int main() {
    int C[60];
    for (int i = 0; i < 60; i++) {
    	cin >> C[i];
    }
    int S;
    cin >> S;
    int T[S], F[S];
    for (int i = 0; i < S; i++) {
    	cin >> T[i] >> F[i];
    }
 
    int cnt = 0;
    vector<int> W;
    double time = 0;
    int people = 0;
    for (int i = 0; i < 60; i++) {
    	for (int j = 0; j < S; j++) {
    		if (i == T[j] - 1) cnt += F[j];
    	}
    	for (int j = 0; j < C[i]; j++) {
    		W.push_back(i+1);
    	}
    	for (; cnt > 0; cnt--) {
    		if (!W.empty()) {
    			time += i+1 - W.front();
    			W.erase(W.begin());
    			people ++;
    		} else break;
    	}
    }
 
    cout << (time/people) << endl;
    return 0;
}