2021 - РЮО - D

#include <bits/stdc++.h>
using namespace std;

const int N = 1e5 + 3;
const int LOG = 18;
int n, x, a[N], mxp[N], p[LOG], dp[LOG][N];

void preCalc() {
    p[0] = 1;
    for (int i = 1; i < LOG; ++i) {
        p[i] = p[i - 1] * 2;
    }
    for (int i = 1, curP = 0, curValue = 1; i < N; ++i) {
        while (curValue * 2 <= i) {
            curValue *= 2;
            curP++;
        }
        mxp[i] = curP;
    }
}

void build() {
    for (int i = 1; i <= n; ++i) {
        dp[0][i] = a[i];
    }
    int Log = mxp[n];
    for (int k = 1; k <= Log; ++k) {
        for (int i = 1; i <= n; ++i) {
            dp[k][i] = min(dp[k - 1][i], dp[k - 1][i + p[k - 1]]);
        }
    }
}

int getMin(int L, int R) {
    int k = mxp[R - L + 1];
    return min(dp[k][L], dp[k][R - p[k] + 1]);
}

void solve() {
    cin >> n >> x;
    for (int i = 1; i <= n; ++i) {
        cin >> a[i];
    }
    build();

    unordered_map<int, vector<int>> ind;

    long long ans = 0;

    for (int i = 1; i <= n; ++i) {
        int R = i;
        int need = (x ^ a[R]);  // a[L] = x ^ a[R];

        if (ind.count(need) > 0) {
            for (int L : ind[need]) {
                ans = max(ans, getMin(L, R) * 1ll * (R - L + 1));
            }
        }

        ind[a[i]].push_back(i);
    }

    cout << ans << endl;
}

int main() {
    ios_base::sync_with_stdio(NULL);
    cin.tie(0); cout.tie(0);

    preCalc();

    int t = 1;
    for (int testId = 1; testId <= t; ++testId) {
        solve();
    }
    return 0;
}