#include<bits/stdc++.h>
#define pb emplace_back
#define AI(i) begin(i), end(i)
using namespace std;
using ll = long long;
template<class T>
bool chmax(T &val, T nv) { return val < nv ? (val = nv, true) : false; }
template<class T>
bool chmin(T &val, T nv) { return nv < val ? (val = nv, true) : false; }
#ifdef KEV
#define DE(args...) kout("[ " + string(#args) + " ] = ", args)
void kout() {cerr << endl;}
template<class T1, class ...T2>
void kout (T1 v, T2 ...e) { cerr << v << ' ', kout(e...); }
template<class T>
void debug(T L, T R) { while (L != R) cerr << *L << " \n"[next(L)==R], ++L; }
#else
#define DE(...) 0
#define debug(...) 0
#endif
// What I should check
// 1. overflow
// 2. corner cases
// Enjoy the problem instead of hurrying to AC
// Good luck !
const int MAX_N = 10000010;

int pn[MAX_N], pl, minp[MAX_N], cnt[MAX_N];

int n, k, a[MAX_N], mxa;

vector<int> getfac(int v) {
    vector<int> res;
    while (v > 1) {
        res.pb(minp[v]);
        while (minp[v] == res.back())
            v /= minp[v];
    }
    return res;
}
// return how many x such that gcd(x, v) > 1
// 不互質
vector<int> getallfac(const vector<int> &fac) {
    int m = fac.size();
    vector<int> dp(1<<m, 1);
    for (int s = 1;s < 1<<m;++s)
        dp[s] = dp[s ^ (1<<__lg(s))] * fac[__lg(s)];
    return dp;
}
int qry(int v) {
    ll res = 0;
    auto pfac = getfac(v);
    auto allfac = getallfac(pfac);
    int m = pfac.size();
    for (int s = 1;s < 1<<m;++s)
        res += cnt[allfac[s]] * (__builtin_popcount(s) & 1 ? 1 : -1);
    return res;
}
int32_t main() {
    ios_base::sync_with_stdio(0), cin.tie(0);
    cin >> n >> k;
    for (int i = 0;i < n;++i)
        cin >> a[i];

    mxa = *max_element(a, a+n);

    for (int i = 2;i <= mxa;++i) {
        if (minp[i] == 0)
            minp[i] = i, pn[pl++] = i;
        for (int j : minp) {
            if (j == 0 || i * j > mxa) break;
            minp[i * j] = j;
            if (i % j == 0) break;
        }
    }

    for (int i = 0;i < n;++i) {
        auto allfac = getallfac(getfac(a[i]));
        for (int f : allfac)
            ++cnt[f];
    }

    // prime numbers and cnt is done

    int midpoint = -1;
    for (int i = 0;i < n;++i) if (qry(a[i]) >= 3) {
        midpoint = i; break;
    }

    if (midpoint == -1) {

    }



}