sqrt-decomposition

#include <cstdio>
#include <iostream>
#include <algorithm>

#define N int(3e4)

using namespace std;

int act[N], len, sz, res[N];

int answer(int l, int r) {
    int ret = -1, i;
    for (i = l; i % sz && i <= r; i++)
        ret = max(ret, act[i]);
    for (; i + sz <= r + 1; i += sz)
        ret = max(ret, res[i / sz]);
    for (; i <= r; i++)
        ret = max(ret, act[i]);
    return ret;
}

int main() {
    int i, m;
    cin >> m;
    for (i = 0; ; i++) {
        cin >> act[i];
        if (act[i] == -1)
            break;
    }
    len = i;

    for (sz = 1; sz * sz < len; sz++);

    for (int j = i + 1; j < sz * sz; j++)
        act[j] = -1;

    for (int i = 0; i < sz * sz; i++)
        res[i / sz] = max(res[i / sz], act[i]);

    for (int i = 0; i + m <= len; i++)
        cout << answer(i, i + m - 1) << endl;

    return 0;
}