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- #pragma GCC optimize("Ofast,no-stack-protector,unroll-loops,fast-math")
- #pragma GCC target("sse,sse2,sse3,ssse3,sse4,sse4.1,sse4.2,popcnt,abm,mmx,avx")
- // #pragma comment(linker, "/stack:200000000"]
- #include <iostream>
- #include <vector>
- #include <cmath>
- #include <algorithm>
- #include <unordered_set>
- #include <unordered_map>
- #include <set>
- #include <map>
- #include <queue>
- #include <deque>
- #include <bitset>
- #include <stack>
- #include <random>
- #include <fstream>
- #include <sstream>
- #include <chrono>
- #define fi first
- #define se second
- #define pb push_back
- #define ll long long
- #define ld long double
- #define hm unordered_map
- #define pii pair<int, int>
- #define sz(a) (int)a.size()
- #define all(a) a.begin(), a.end()
- #define cinv(v) for (auto& x: v) cin >> x
- #define fr(i, n) for (int i = 0; i < n; ++i)
- #define fl(i, l, n) for (int i = l; i < n; ++i)
- #define int ll
- using namespace std;
- #ifdef __LOCAL
- #define dbg(x) cerr << #x << " : " << x << '\n'
- const int maxn = 400 + 20;
- #else
- #define dbg(x)
- const int maxn = 400 + 20;
- #endif
- //tg: @galebickosikasa
- const ll inf = (ll) 2e9;
- const ld pi = asin (1) * 2;
- const ld eps = 1e-8;
- const ll mod = (ll)1e9 + 7;
- const ll ns = 97;
- const int C = 200;
- mt19937 rnd(chrono::steady_clock::now().time_since_epoch().count());
- struct edge {
- int to, c, f;
- };
- vector<edge> edges;
- vector<int> g[maxn];
- int it[maxn], d[maxn], used[maxn];
- int timer = 1;
- int bfs (int s, int t, int x) {
- for (auto& x: d) x = inf;
- d[s] = 0;
- queue<int> a;
- a.push (s);
- while (!a.empty ()) {
- int v = a.front ();
- a.pop ();
- // dbg (v);
- for (auto& u: g[v]) {
- auto& e = edges[u];
- // dbg (e.to);
- if (d[e.to] == inf && e.c - e.f >= x) {
- d[e.to] = d[v] + 1;
- a.push (e.to);
- }
- }
- }
- return d[t] < inf;
- }
- int dfs (int v, int t, int start, int x, int cnt = 0, int c = inf, int p = -1) {
- dbg (v);
- dbg (start);
- if (v == t && p - C == start && cnt > 5) return c;
- if (v == t) return 0;
- used[v] = timer;
- if (p == 400) start = v;
- for (auto& u: g[v]) {
- auto& e = edges[u];
- if ((e.to != start + C && used[e.to] == timer) || e.c - e.f < x) {
- continue;
- }
- int delta = dfs (e.to, t, start, x, cnt + 1, min (c, e.c - e.f), v);
- if (delta > 0) {
- auto& _e = edges[u^1];
- e.f += delta;
- _e.f -= delta;
- return delta;
- }
- }
- return 0;
- }
- int kek (int x) {
- for (int i = 2; i * i <= x; ++i) {
- if (x % i == 0) return 0;
- }
- return 1;
- }
- signed main () {
- ios_base::sync_with_stdio(false);
- cin.tie(nullptr);
- cout.tie(nullptr);
- int n;
- cin >> n;
- vector<int> goo (n);
- cinv (goo);
- fr (i, n) {
- fr (j, n) {
- if (i == j) continue;
- if (kek (goo[i] + goo[j])) {
- g[i].pb (sz (edges));
- edges.pb ({j + C, 1, 0});
- g[j + C].pb (sz (edges));
- edges.pb ({i, 0, 0});
- }
- }
- }
- int s = 400, t = 400 + 1;
- fr (i, n) {
- g[s].pb (sz (edges));
- edges.pb ({i, 1, 0});
- g[i].pb (sz (edges));
- edges.pb ({s, 0, 0});
- g[i + C].pb (sz (edges));
- edges.pb ({t, 1, 0});
- g[t].pb (sz (edges));
- edges.pb ({i + C, 0, 0});
- g[i + C].pb (sz (edges));
- edges.pb ({i, 1, 0});
- g[i].pb (sz (edges));
- edges.pb ({i + C, 0, 0});
- }
- while (dfs (s, t, -1, 1)) {
- dbg ("kek");
- ++timer;
- }
- ++timer;
- dbg ("kek");
- vector<vector<int>> ans;
- fr (i, n) {
- if (used[i] < timer) {
- int v = i;
- vector<int> t;
- for (auto& x: g[i]) {
- if (edges[x].f == 1) {
- v = edges[x].to - C;
- break;
- }
- }
- if (v == i) {
- cout << "Impossible\n";
- exit (0);
- }
- t.pb (i);
- while (v != i) {
- // dbg (v);
- t.pb (v);
- for (auto& x: g[v]) {
- if (edges[x].f == 1) {
- v = edges[x].to - C;
- }
- }
- if (v == t.back ()) {
- cout << "Impossible\n";
- exit (0);
- }
- }
- for (auto& x: t) used[x] = timer;
- ans.pb (t);
- }
- }
- cout << sz (ans) << '\n';
- for (auto& v: ans) {
- for (auto& x: v) cout << x + 1 << ' ';
- cout << '\n';
- }
- }
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