题解 | 大整数哈希

import java.util.*;

public class Main {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);

        int n = sc.nextInt();

        Map<Long, Long> f = new HashMap<>();
        long total = 0;

        for (int i = 1; i <= n; i++) {
            // ❌ 错误：sc.nextLong() 无法解析 > 2^63-1 的数
            // ✅ 正确：先读字符串，再 parseUnsignedLong
            String xStr = sc.next();
            String yStr = sc.next();
            long x = Long.parseUnsignedLong(xStr);
            long y = Long.parseUnsignedLong(yStr);

            long ans_i = f.getOrDefault(x, 0L);

            total += (long) i * ans_i; // 自动 mod 2^64

            f.put(x, y);
        }

        // 输出必须用无符号形式
        System.out.println(Long.toUnsignedString(total));

        sc.close();
    }
}