携程笔试第四题为什么0分？

import java.io.*;
import java.util.ArrayDeque;
import java.util.Deque;

public class Main {
    private static long n, k, sum, intervalSum, res;
    private static final int N = 100010;
    private static long[] a = new long[N], s = new long[N];
    private static Deque<Long[]> q = new ArrayDeque<>();
    public static void main(String[] args) throws IOException {
        BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
        BufferedWriter bw = new BufferedWriter(new OutputStreamWriter(System.out));
        String[] in = br.readLine().split(" ");
        n = Long.valueOf(in[0]);
        k = Long.valueOf(in[1]);
        sum = Long.valueOf(in[2]);
        in = br.readLine().split(" ");
        for (int i = 1; i <= n; i++) {
            a[i] = Long.valueOf(in[i - 1]);
        }
        intervalSum = calculateSum(1, (int) k);
        processFirstInterval();
        for (int i = (int) k + 1; i <= n; i++) {
//            bw.write("first interval sum : " + intervalSum + "\n");
            // 滑动窗口
            intervalSum -= q.pollFirst()[0];
//            bw.write(q.peekFirst()[0] + " ");
            q.offerLast(new Long[]{a[i], (long) i});
            intervalSum += q.peekLast()[0];
//            bw.write("interval sum : " + intervalSum + "\n");
            // 处理超过sum的情况
            if (intervalSum > sum) {
                a[i] -= intervalSum - sum;
                res += intervalSum - sum;
                q.pollLast();
                q.offerLast(new Long[]{a[i], (long) i});
            }
        }
//        for (int i = 1; i <= n; i++) {
//            bw.write(String.format("%d ", a[i]));
//        }
        bw.write(res + "");
        bw.flush();
    }
    private static long calculateSum(int st, int ed) {
        long res = 0L;
        for (int i = st; i <= ed; i++) {
            res += a[i];
        }
        return res;
    }

    private static void processFirstInterval() {
        int tail = (int) k;
        if (intervalSum <= sum) {
            return;
        }
        while (intervalSum - sum >= a[tail]) {
            intervalSum -= a[tail];
            res += a[tail];
            a[tail--] = 0;
        }
        if (intervalSum - sum < a[tail]) {
            res += intervalSum - sum;
            a[tail] -= intervalSum - sum;
            intervalSum = sum;
        }
        for (int i = 1; i <= k; i++) {
            q.offerLast(new Long[]{a[i], (long) i});
        }
    }
}

我自测样例：

5 4 10

9 7 3 6 5

答案难道不是15？我想破脑袋也想不出来15以外的答案。