import java.util.*;
import java.util.stream.*;

class Main {
    private String from;
    public String getFrom() { return from; }
    private String to;
    public String getTo() { return to; }
    private String currency;
    public String getCurrency() { return currency; }
    private int amount;
    public int getAmount() { return amount; }
    public Main(String from, String to, String currency, int amount) {
        this.from = from;
        this.to = to;
        this.currency = currency;
        this.amount = amount;
    }

    @Override
    public String toString() {
        return "Main{" +
                "from='" + from + '\'' +
                ", to='" + to + '\'' +
                ", currency='" + currency + '\'' +
                ", amount=" + amount +
                '}';
    }
}
class L14 {
    public static void main(String[] args) {
        List<Main> txns = new LinkedList<>();
        txns.add(new Main("Alice","Bob",   "USD",  10));
        txns.add(new Main("Bob","Charlie", "USD",   5));
        txns.add(new Main("Dave","Charlie","EUR",   5));
        txns.add(new Main("Eve","Frank",   "RUB", 500));
        System.out.println(txns);
        // 1
        // Посчитать баланс транзакций по людям
        // A: -10, B: 5, C: 10, D: -5, E: -500, F: 500
        // Main{from='Alice', to='Bob', currency='USD', amount=10} -> {"Alice"=-10}, {"Bob"=10}
        TreeMap<String, Integer> balances = new L14().run(txns);

        // Вывести

        for (Map.Entry<String, Integer> entry : balances.entrySet()) {
            System.out.println(entry.getKey() + ": " + entry.getValue());
        }


    }
    public TreeMap<String, Integer> run(List<Main> txns) {
        Map<String, Integer> balances = txns.stream()
                .flatMap(t -> Stream.of(
                        new TreeMap.SimpleEntry<>(t.getFrom(), -t.getAmount()),
                        new TreeMap.SimpleEntry<>(t.getTo(), t.getAmount())))
                .collect(Collectors.toMap(Map.Entry::getKey, Map.Entry::getValue, (a,b) -> a+b));

        TreeMap<String, Integer> ar = new TreeMap<>();
        for (Map.Entry<String, Integer> entry: balances.entrySet()) {
            ar.put(entry.getKey(), entry.getValue());
        }
        return ar;
    }
}