#include <bits/stdc++.h>

using namespace std;

string ltrim(const string &);
string rtrim(const string &);
vector<string> split(const string &);

enum struct OutputMode { HackerRank, Linux };

OutputMode outputMode = OutputMode::Linux;

/*
 * Complete the 'weightedMean' function below.
 *
 * The function accepts following parameters:
 *  1. INTEGER_ARRAY X
 *  2. INTEGER_ARRAY W
 */

void weightedMean(vector<int> X, vector<int> W) {
    int numerator = 0, denominator = 0;    
    for (size_t i = 0; i < X.size(); i++)
    {
        numerator += X[i] * W[i];
        denominator += W[i];
    }
    cout << fixed << setprecision(1) << numerator/double(denominator) << endl;
}

int main()
{
    string n_temp;
    int n;

    if (outputMode == OutputMode::HackerRank)
    {
        getline(cin, n_temp);
        n = stoi(ltrim(rtrim(n_temp)));
    }
    else
        n = 5;
    
    string vals_temp_temp;
    if (outputMode == OutputMode::HackerRank)
        getline(cin, vals_temp_temp);
    else
        vals_temp_temp = "10 40 30 50 20";
        

    vector<string> vals_temp = split(rtrim(vals_temp_temp));

    vector<int> vals(n);

    for (int i = 0; i < n; i++) {
        int vals_item = stoi(vals_temp[i]);

        vals[i] = vals_item;
    }

    string weights_temp_temp;
    if (outputMode == OutputMode::HackerRank)
        getline(cin, weights_temp_temp);
    else
        weights_temp_temp = "1 2 3 4 5";

    vector<string> weights_temp = split(rtrim(weights_temp_temp));

    vector<int> weights(n);

    for (int i = 0; i < n; i++) {
        int weights_item = stoi(weights_temp[i]);

        weights[i] = weights_item;
    }

    weightedMean(vals, weights);

    return 0;
}

std::function<int(int)> f_isspace = [](int x){ return isspace(x); };

string ltrim(const string &str) {
    string s(str);

    s.erase(
        s.begin(),
        find_if(s.begin(), s.end(), not_fn(f_isspace))
        );

    return s;
}

string rtrim(const string &str) {
    string s(str);

    s.erase(
        find_if(s.rbegin(), s.rend(), not_fn(f_isspace)).base(),
        s.end()
        );

    return s;
}

vector<string> split(const string &str) {
    vector<string> tokens;

    string::size_type start = 0;
    string::size_type end = 0;

    while ((end = str.find(" ", start)) != string::npos) {
        tokens.push_back(str.substr(start, end - start));

        start = end + 1;
    }

    tokens.push_back(str.substr(start));

    return tokens;
}