#include <bits/stdc++.h>   using namespace std;   const int MAXV = 210;   const int MAXE = 40010;   const int inf = 1e9;   struct Edge {     int u, v, cap, flow, next;   } grana[MAXE];   int n, m, E;   vector<int> odd, even, sol[MAXV], g[MAXV];   int head[MAXV], dist[MAXV];   int src, snk, k;   bool mark[MAXV];   int val[MAXV], a[MAXV];   bool is_prime(int x) {     int rt = sqrt(x);     for (int i = 2; i <= rt; i++)       if (x % i == 0) return false;     return true;   }   void add_edge(int u, int v, int c1, int c2) {     grana[E++] = (Edge){u, v, c1, 0, head[u]};     head[u] = E - 1;     grana[E++] = (Edge){v, u, c2, 0, head[v]};     head[v] = E - 1;   }   bool bfs() {     fill(dist, dist + MAXV, -1);     queue<int> q;     dist[src] = 0;     for (q.push(src); !q.empty(); q.pop()) {       int u = q.front();       for (int e = head[u]; e != -1; e = grana[e].next) {         int v = grana[e].v;         if (grana[e].cap > grana[e].flow && dist[v] == -1) {           dist[v] = dist[u] + 1;           q.push(v);         }       }     }     return (dist[snk] != -1);   }   int dfs(int u, int minCap) {     if (minCap == 0) return 0;     if (u == snk) return minCap;     for (int e = head[u]; e != -1; e = grana[e].next) {       int v = grana[e].v;       if (dist[v] != dist[u] + 1) continue;       int augment = dfs(v, min(minCap, grana[e].cap - grana[e].flow));       if (augment) {         grana[e].flow += augment;         grana[e ^ 1].flow -= augment;         return augment;       }     }     return 0;   }   int Dinic() {     int flow = 0, bf = 0;     while (bfs()) {       do {         bf = dfs(src, inf);         flow += bf;       } while (bf);     }     return flow;   }   void fail() {     printf( Impossible );     exit(0);   }   void traversal(int u, int num) {     mark[u] = true;     sol[num].push_back(val[u]);     for (int i = 0; i < 2; i++) {       int v = g[u][i];       if (!mark[v]) {         traversal(v, num);         return;       }     }   }   int main() {     fill(head, head + MAXV, -1);     scanf( %d , &n);     for (int i = 0; i < n; i++) {       int x;       scanf( %d , &x);       a[i] = x;       if (x & 1)         odd.push_back(x);       else         even.push_back(x);     }     if (odd.size() != even.size()) fail();     src = n, snk = n + 1;     for (int i = 0; i < even.size(); i++) {       for (int j = 0; j < odd.size(); j++) {         if (is_prime(even[i] + odd[j])) {           add_edge(i, even.size() + j, 1, 0);         }       }     }     for (int i = 0; i < even.size(); i++) add_edge(src, i, 2, 0);     for (int i = 0; i < odd.size(); i++) add_edge(even.size() + i, snk, 2, 0);     int maxFlow = Dinic();     if (maxFlow < n) fail();     for (int i = 0; i < even.size(); i++) {       for (int e = head[i]; e != -1; e = grana[e].next) {         if (grana[e].flow == 1) {           g[i].push_back(grana[e].v);           g[grana[e].v].push_back(i);         }       }     }     int p = 0;     for (int i = 0; i < even.size(); i++) {       while (a[p] != even[i]) p++;       val[i] = p + 1;       p++;     }     p = 0;     for (int i = 0; i < odd.size(); i++) {       while (a[p] != odd[i]) p++;       val[(int)(even.size()) + i] = p + 1;       p++;     }     for (int i = 0; i < n; i++)       if (!mark[i]) traversal(i, k++);     printf( %d n , k);     for (int i = 0; i < k; i++) {       printf( %d  , sol[i].size());       for (auto xt : sol[i]) printf( %d  , xt);       printf(  n );     }     return 0;   }