#include <cstdio>
#include <iostream>
#include <vector>

#include <random>

#define _rep(_1, _2, _3, _4, name, ...) name
#define rep2(i, n) rep3(i, 0, n)
#define rep3(i, a, b) rep4(i, a, b, 1)
#define rep4(i, a, b, c) for (int i = int(a); i < int(b); i += int(c))
#define rep(...) _rep(__VA_ARGS__, rep4, rep3, rep2, _)(__VA_ARGS__)

using namespace std;
using i8 = signed char;
using i64 = long long;

template <typename WeightType>
class MaximumWeightedMatching {
  /*
  Maximum Weighted Matching in General Graphs
  - O(n^3) time
  - O(n + m) space

  Note: each vertex is 1-indexed.
  */
public:
  using weight_t = WeightType;
  using weight_sum_t = i64;
  struct Edge { int from, to; weight_t weight; };

private:
  enum TreeLabelNumber { INNER = -1, UNUSED = 0, OUTER = 1 };
  enum LabelNumber { SEPARATED = -2, DEFAULT = -1 };
  enum EdgeNumber { UNDEFINED = 1 << 30};

  const  weight_t INF = weight_t(1) << (sizeof(weight_t) * 8 - 2);

  struct Node { int next, from, to; };
  struct Label { int from, to; };
  struct LinkedList { int eid, next; };

  class Queue {
  public:
    Queue() {}
    Queue(int N) : que(N), qh(0), qt(0) {}
    void clear() { qh = qt = 0; }
    int* data() { return que.data(); }
    bool empty() const { return qh == qt; }
    int dequeue() { return que[qh++]; }
    void enqueue(int u) { que[qt++] = u; }
    int operator [] (int i) const { return que[i]; }
    int size() const { return qt; }

    vector<int> que;
    int qh, qt;
  };

public:
  MaximumWeightedMatching(int N, const vector<Edge>& raw_edges)
      : N(N), B((N - 1) / 2), size(N + B + 1) {

    offsets.assign(N + 2, 0);
    for (auto& e : raw_edges) {
      offsets[e.from + 1]++;
      offsets[e.to + 1]++;
    }
    rep(i, 1, N + 1) offsets[i] += offsets[i - 1];
    edges.resize(raw_edges.size() * 2);
    rep(i, raw_edges.size()) {
      auto& e = raw_edges[i];
      edges[offsets[e.from]++] = {e.from, e.to, 2 * e.weight};
      edges[offsets[e.to]++] = {e.to, e.from, 2 * e.weight};
    }
    rep(i, N + 1) offsets[N + 1 - i] = offsets[N - i];
    offsets[0] = 0;
  }

  weight_sum_t maximum_weighted_matching() {
    initialize();
    set_potential();
    rep(u, 1, N + 1) if (!mate[u]) {
      for (int s = 0; !augmented(u, s); s = adjust_dual_solutions());
      fix_blossom_bases();
      clear_label();
    }
    weight_sum_t ret = 0;
    rep(u, 1, N + 1) if (mate[u] > u) {
      weight_t max_w = 0;
      rep(eid, offsets[u], offsets[u + 1]) if (edges[eid].to == mate[u]) {
        max_w = max(max_w, edges[eid].weight);
      }
      ret += max_w;
    }
    return ret >> 1;
  }

private:
  inline int encode(int e) const {
    return e + size + 1; // should be >= 3
  }

  inline weight_t reduced_cost(int u, int v, const Edge& e) const {
    return potential[u] + potential[v] - e.weight;
  }

  inline weight_t reduced_cost(int eid) const {
    return reduced_cost(edges[eid].from, edges[eid].to, edges[eid]);
  }

  void rematch(int v, int w) {
    auto t = mate[v]; mate[v] = w;
    if (mate[t] != v) return;
    if (label[v].to == 0) {
      mate[t] = label[v].from;
      rematch(mate[t], t);
    } else {
      int x = label[v].from, y = label[v].to;
      rematch(x, y); rematch(y, x);
    }
  }

  Label search_blossom_edge(int bid) const {
    int b = base[bid], bv = b;
    for (; node[bv].next != b; bv = node[node[bv].next].next);
    return {node[bv].from, node[bv].to};
  }

  void label_blossom(int bid, int m, Label l) {
    label[bid] = {l.from, (l.to == surface[l.to]) ? 0 : l.to};
    if (bid <= N) return;
    int b = base[bid]; label_blossom(b, mate[bid] = m, l);
    l = search_blossom_edge(bid);
    for (int bv = b, bw; node[bv].next != b; bv = node[bw].next) {
      label_blossom(bw = node[bv].next, 0, l);
      label_blossom(node[bw].next, node[bw].from, {node[bv].from, node[bv].to});
    }
  }

  int find_mate(int bid) {
    return bid <= N ? mate[bid] : mate[bid] = find_mate(base[bid]);
  }

  void push_inner_blossom_rec(int bid, bool push=true) {
    tree_label[bid] = (bid <= N) ? INNER : UNUSED;
    if (bid > N) {
      int v = base[bid], u = v;
      do { push_inner_blossom_rec(v, push); } while ( (v = node[v].next) != u);
    } else if (push) inner_vertices[inner_vertices_size++] = bid;
  }

  void push_inner_blossom(int bid) {
    if (tree_label[bid] != UNUSED) return;
    bool push = label[bid].from != SEPARATED;
    if (bid > N) {
      if (push) inner_blossoms[inner_blossom_size++] = bid;
      push_inner_blossom_rec(bid, push);
    } else if (push) inner_vertices[inner_vertices_size++] = bid;
    tree_label[bid] = INNER;
  }

  void push_outer_blossom_rec(int bid) {
    tree_label[bid] = (bid <= N) ? OUTER : UNUSED;
    if (bid > N) {
      int v = base[bid], u = v;
      do { push_outer_blossom_rec(v); } while ( (v = node[v].next) != u );
    } else outer_vertices.enqueue(bid);
  }

  void push_outer_blossom(int bid, bool push) {
    push_outer_blossom_rec(bid);
    if (bid <= N) return;
    if (push) outer_blossoms[outer_blossom_size++] = bid, tree_label[bid] = OUTER;
    else tree_label[bid] = UNUSED;
  }

  inline void merge_edge(int x, int bx, int eid) {
    auto& e = edges[eid];
    int y = e.to, by = surface[y];
    if (tree_label[by] != OUTER || bx == by) return;
    auto r_cost = reduced_cost(x, y, e);
    if (r_cost < best_cost[by].first) {
      if (best_cost[by].first == INF) merged_edges[merged_edge_size++] = by;
      best_cost[by] = {r_cost, eid};
    }
  }

  inline void merge_vertex(int x, int bx) {
    rep(eid, offsets[x], offsets[x + 1]) merge_edge(x, bx, eid);
    best_edge[x] = UNDEFINED;
  }

  void clear_best_edges(int b) {
    if (b > N) {
      int v = b = base[b];
      do { clear_best_edges(v); } while ( (v = node[v].next) != b );
    } else best_edge[b] = UNDEFINED;
  }

  void merge_outer(int b, int bid) {
    if (b > N) {
      for (int head = blist_head[b]; head >= 0; head = bnode[head].next) {
        int eid = bnode[head].eid;
        merge_edge(edges[eid].from, bid, eid);
        next_bnode.push_back(head);
      }
      blist_head[b] = -1;
      clear_best_edges(b);
    } else merge_vertex(b, bid);
  }

  void merge_inner(int b, int bid) {
    if (b > N) {
      int v = b = base[b];
      do { merge_inner(v, bid); } while ((v = node[v].next) != b);
    } else merge_vertex(b, bid);
  }

  void build_linked_list(int bid) {
    if (bid <= N) return;
    int last = -1;
    for (; merged_edge_size > 0; ) {
      int nid = next_bnode.back(); next_bnode.pop_back();
      int by = merged_edges[--merged_edge_size], eid = best_cost[by].second;
      int x = edges[eid].from, y = edges[eid].to;
      bnode[nid] = {eid, last};
      if (tree_label[y] == OUTER) update_best_edge(y, by, best_cost[by].first, eid);
      if (best_edge[x] == UNDEFINED || best_cost[by].first < reduced_cost(best_edge[x])) {
        best_edge[x] = eid;
      }
      best_cost[by] = {INF, UNDEFINED};
      last = nid;
    }
    blist_head[bid] = last;
  }

  void merge_best_edges(int bid, int inner_count) {
    rep(i, inner_count) {
      int bv = outer_blossoms[outer_blossom_size + i];
      if (bv >= 0) merge_outer(bv, bid), merge_inner(node[bv].next, bid);
      else merge_inner(~bv, bid), merge_outer(node[~bv].next, bid);
    }
    merge_outer(base[bid], bid);
    build_linked_list(bid);
  }

  void contract(int x, int y, int eid) {
    int s = surface[x], t = surface[y];
    if (s == t) return;
    auto h = label[surface[mate[s]]].from = label[surface[mate[t]]].from = -encode(eid);

    int lca = -1;
    for (; ; label[surface[mate[s]]].from = h) {
      if (mate[t] != 0) swap(s, t);
      s = lca = surface[label[s].from];
      if (label[surface[mate[s]]].from == h) break;
    }

    int inner_count = 0;
    for (int dir = 0; dir < 2; ++dir) {
      int v = (dir == 0) ? x : y;
      while (1) {
        int bv = surface[v], mv = mate[bv], bmv = surface[mv];
        if (bv == lca) break;
        label[mv] = label[bmv] = {x, y};
        auto n = node[bmv];
        if (!dir) {
          node[bv] = {bmv, mate[mv], mv};
          node[bmv].next = surface[n.to];
        } else {
          node[surface[n.to]] = {bmv, n.to, n.from};
          node[bmv] = {bv, mv, mate[mv]};
        }
        push_outer_blossom(bmv, false);
        v = label[bv].from;

        // Caution: used as temporary array
        outer_blossoms[outer_blossom_size + (inner_count++)] = !dir ? bv : ~bmv;
      }
    }
    node[surface[y]] = {surface[x], y, x};

    int bid = next_bid.back(); next_bid.pop_back();
    base[bid] = lca, label[bid].from = label[lca].from, mate[bid] = mate[lca];

    tree_label[bid] = OUTER;
    set_surface(bid, bid);
    merge_best_edges(bid, inner_count);

    outer_blossoms[outer_blossom_size++] = bid;
  }

  inline void update_best_edge(int y, int by, weight_t r_cost, int eid) {
    if (tree_label[by] != OUTER && best_edge[y] == UNDEFINED) {
      neighbors[neighbor_size++] = y;
    }
    if (best_edge[y] == UNDEFINED || r_cost < reduced_cost(best_edge[y])) {
      best_edge[y] = eid;
    }
  }

  void build_edge_list(int b) {
    if (b <= N) return;
    merge_inner(b, b);
    build_linked_list(b);
  }

  bool augmented(int root, int s) {
    if (s == 0) {
      int br = surface[root];
      push_outer_blossom(br, true);
      label_blossom(br, 0, {0, 0});
      build_edge_list(br);
    }
    for (; !outer_vertices.empty() || s > 0; s = 0) {
      auto x = (s > 0) ? s : outer_vertices.dequeue();
      if (potential[x] == 0) {
        if (root != x) rematch(x, 0);
        return true;
      }
      rep(eid, offsets[x], offsets[x + 1]) {
        int bx = surface[x], y = edges[eid].to, by = surface[y];
        if (bx == by) continue;
        auto r_cost = reduced_cost(x, y, edges[eid]);
        if (r_cost > 0 || tree_label[by] != OUTER) {
          update_best_edge(y, by, r_cost, eid);
          if (r_cost > 0) continue;
        }
        if (label[by].from >= 0) {
          contract(x, y, eid);
          continue;
        }
        if (tree_label[by] == UNUSED) {
          push_inner_blossom(by);
          if (by != y) label_blossom(by, find_mate(by), {DEFAULT, 0});
        }
        int z = mate[by];
        if (z == 0 && by != surface[root]) {
          rematch(x, y); rematch(y, x);
          return true;
        }
        int bz = surface[z];
        if (label[bz].from < 0) {
          node[by] = {-1, y, x};
          push_outer_blossom(bz, true);
          label_blossom(bz, mate[z], {x, y});
          build_edge_list(bz);
        }
      }
    }
    return false;
  }

  void set_surface(int b, int bid) {
    for (int v = base[b]; surface[v] != bid; v = node[v].next) {
      if (v > N) tree_label[v] = UNUSED, set_surface(v, bid);
      surface[v] = bid;
    }
  }

  void reset_surface(int b, int bid) {
    surface[b] = bid;
    if (b <= N) return;
    for (b = base[b]; surface[b] != bid; b = node[b].next) reset_surface(b, bid);
  }

  void separate_blossom(int bid, bool push_blossom=true) {
    tree_label[bid] = UNUSED, label[bid].from = SEPARATED;
    if (bid <= N) return;
    if (push_blossom) inner_blossoms[inner_blossom_size++] = bid;
    for (int b = base[bid]; label[b].from != SEPARATED; b = node[b].next) {
      separate_blossom(b, false);
    }
  }

  void reverse_blossom(int b) {
    int v = b, fr = node[b].from, to = node[b].to;
    for (int nv = node[v].next; nv != b; ) {
      int nnext = node[nv].next, nfr = node[nv].from, nto = node[nv].to;
      node[nv].next = v, node[nv].from = to, node[nv].to = fr;
      fr = nfr, to = nto, v = nv, nv = nnext;
    }
    node[b].next = v, node[b].from = to, node[b].to = fr;
  }

  void expand_blossom(int bid) {
    next_bid.push_back(bid); tree_label[bid] = UNUSED;
    for (int b = base[bid]; surface[b] == bid; b = node[b].next) reset_surface(b, b);
    int old_base = base[bid], target = surface[node[bid].from];
    if (mate[node[target].from] == node[target].to) reverse_blossom(old_base);
    for (int b = target; node[b].next != old_base; ) {
      separate_blossom(b = node[b].next); separate_blossom(b = node[b].next);
    }
    node[target] = node[bid];
    for (int b = old_base; ; b = node[b].next) {
      label[b].from = DEFAULT, tree_label[b] = INNER;
      if (b > N) inner_blossoms[inner_blossom_size++] = b;
      int m = find_mate(b), bm = surface[m];
      if (b != old_base) mate[bm] = mate[m];
      label[m] = label[bm] = {node[b].to, node[b].from};
      if (b == target) break;
      push_outer_blossom(b = node[b].next, true);
      build_edge_list(b);
    }
    base[bid] = bid, surface[bid] = bid;
  }

  void update_potential(int* vs, int s, weight_t delta, int label) {
    rep(i, s) {
      int x = vs[i];
      if (tree_label[x] != label) continue;
      potential[x] += delta;
    }
  }

  int adjust_dual_solutions() {
    pair<weight_t, int> delta1(INF, 0), delta2(INF, 0), delta3(INF, 0), delta4(INF, 0);
    rep(i, outer_vertices.size()) {
      int y = outer_vertices[i], eid = best_edge[y];
      delta1 = min(delta1, {potential[y], y});
      if (eid != UNDEFINED) {
        delta3 = min(delta3, {reduced_cost(eid) >> 1, y});
      }
    }
    rep(i, neighbor_size) {
      int y = neighbors[i];
      if (tree_label[y] == UNUSED) {
        int eid = best_edge[y], x = edges[eid].from;
        delta2 = min(delta2, {reduced_cost(x, y, edges[eid]), x});
      }
    }
    rep(i, inner_blossom_size) if (tree_label[inner_blossoms[i]] == INNER) {
      int b = inner_blossoms[i];
      delta4 = min(delta4, {potential[b] >> 1, b});
    }
    auto delta = min(min(delta1, delta2), min(delta3, delta4));
    auto d = delta.first;
    update_potential(outer_vertices.data(), outer_vertices.size(), -1 * d, OUTER);
    update_potential(inner_vertices.data(), inner_vertices_size,    1 * d, INNER);
    update_potential(outer_blossoms.data(), outer_blossom_size,     2 * d, OUTER);
    update_potential(inner_blossoms.data(), inner_blossom_size,    -2 * d, INNER);
    if (delta4.first == d) {
      expand_blossom(delta4.second);
      return -1;
    } else {
      return delta.second;
    }
  }

  void fix_blossom_bases() {
    int remain = size - next_bid.size() - (N + 1);
    for (int bid = N + 1; bid < size && remain > 0; ++bid) if (base[bid] != bid) {
      int b = base[bid];
      for (int skipped = 0; skipped < 2;) {
        b = node[b].next;
        if (mate[node[b].from] == node[b].to) skipped = 0;
        else skipped++;
      }
      base[bid] = b;
      --remain;
    }
  }

  void free_edge_list(int x) {
    for (int head = blist_head[x]; head >= 0; head = bnode[head].next) {
      next_bnode.push_back(head);
    }
    blist_head[x] = -1;
  }

  void clear_vertices(int* vs, int size) {
    rep(i, size) {
      int v = vs[i];
      label[v] = {DEFAULT, 0}; tree_label[v] = UNUSED; best_edge[v] = UNDEFINED;
    }
  }

  void clear_label() {
    label[0] = {DEFAULT, 0};
    clear_vertices(outer_vertices.data(), outer_vertices.size()); outer_vertices.clear();
    clear_vertices(inner_vertices.data(), inner_vertices_size); inner_vertices_size = 0;
    clear_vertices(outer_blossoms.data(), outer_blossom_size);
    rep(i, outer_blossom_size) if (blist_head[outer_blossoms[i]] >= 0) free_edge_list(outer_blossoms[i]);
    outer_blossom_size = 0;
    clear_vertices(inner_blossoms.data(), inner_blossom_size); inner_blossom_size = 0;
    rep(i, neighbor_size) best_edge[neighbors[i]] = UNDEFINED;
    neighbor_size = 0;
  }

  void set_potential() {
    potential.resize(size);
    rep(u, 1, N + 1) {
      weight_t max_w = 0;
      rep(eid, offsets[u], offsets[u + 1]) max_w = max(max_w, edges[eid].weight);
      potential[u] = max_w >> 1;
    }
  }

  void initialize() {
    mate.assign(size, 0);
    label.assign(size, {-1, 0});

    surface.resize(size); rep(i, size) surface[i] = i;
    base.resize(size); rep(i, size) base[i] = i;
    node.resize(size); rep(i, size) node[i] = {i, i, i};

    outer_vertices = Queue(N);
    inner_vertices.resize(N + 1); inner_vertices_size = 0;
    outer_blossoms.resize(B); outer_blossom_size = 0;
    inner_blossoms.resize(B); inner_blossom_size = 0;

    tree_label.assign(size, UNUSED);

    next_bid.resize(B);
    rep(i, B) next_bid[i] = size - 1 - i;

    merged_edges.resize(N + 1); merged_edge_size = 0;
    best_cost.assign(size, {INF, UNDEFINED});

    neighbors.resize(N + 1); neighbor_size = 0;
    best_edge.assign(size, UNDEFINED);

    blist_head.assign(size, -1);
    next_bnode.resize(edges.size());
    rep(i, edges.size()) next_bnode[i] = edges.size() - 1 - i;

    bnode.resize(edges.size());
  }

private:
  int N, B, size;
  vector<Edge> edges;
  vector<int> offsets;

  vector<Label> label;
  vector<int> mate, surface, base;
  vector<Node> node;
  vector<weight_t> potential;

  vector<int> next_bid;

  vector<i8> tree_label;

  Queue outer_vertices;
  vector<int> inner_vertices; int inner_vertices_size;
  vector<int> outer_blossoms; int outer_blossom_size;
  vector<int> inner_blossoms; int inner_blossom_size;

  vector<int> merged_edges; int merged_edge_size;
  vector< pair<weight_t, int> > best_cost;
  vector<int> neighbors; int neighbor_size;
  vector<int> best_edge;

  vector<int> blist_head;
  vector<LinkedList> bnode;
  vector<int> next_bnode;
};

const int MAX_P=11111111;
bool prime[MAX_P];

#include<set>
#include<algorithm>
int main() {
    fill_n(prime,MAX_P,1);
    prime[0]=prime[1]=0;
    for(int i=2;i<MAX_P;i++){
        if(!prime[i])continue;
        for(int j=i+i;j<MAX_P;j+=i)prime[j]=0;
    }
    int N;
    cin>>N;
    vector<int>X(N);
    rep(i,N)cin>>X[i];

    set<int>xs;
    rep(i,N)xs.insert(X[i]);

    vector<int> A;
    rep(i,N){
        if(xs.find(X[i]-1)==xs.end())A.push_back(X[i]);
        if(xs.find(X[i]+1)==xs.end())A.push_back(X[i]+1);
    }

    sort(A.begin(),A.end());

  using Edge = MaximumWeightedMatching<int>::Edge;
  vector<Edge> edges;
  rep(i,A.size())for(int j=i+1;j<A.size();j++){
    int cost;
    int d=A[j]-A[i];
    if(d%2&&prime[d])cost=1;
    else if(d%2==0)cost=2;
    else cost=3;
    cost=5-cost;
    edges.push_back({i+1,j+1,cost});
  }
  auto MWM = MaximumWeightedMatching<int>(A.size(), edges);
  auto ans = MWM.maximum_weighted_matching();

    cout<<-ans+5*(A.size()/2)<<endl;
}


Measured memory_bytes: 12412