// This piece of code is a pile of sh!t
#include <iostream>
#include <list>
using namespace std;

class Graph{
private:
    int Number_Of_Vertices;
    int Number_Of_Edges;
    int Euler_Determinant;
    bool *Determinant_aux;
    list<int> *adjacent_nodes;
public:
    Graph(int _Number_Of_Vertices, int _Number_Of_Edges){
        Euler_Determinant = 0;
        Number_Of_Vertices = _Number_Of_Vertices;
        Number_Of_Edges = _Number_Of_Edges;
        adjacent_nodes = new list<int>[_Number_Of_Vertices];
        Determinant_aux = new bool [_Number_Of_Vertices];
        for (int i=0;i<_Number_Of_Vertices;i++){
            Determinant_aux[i]=0;
        }
    }

    void AddEdge(int v, int w){
        adjacent_nodes[v].push_back(w);
        adjacent_nodes[w].push_back(v);
        if (Determinant_aux[v]) {Determinant_aux[v] = 0;Euler_Determinant--;}
        else {Determinant_aux[v] = 1; Euler_Determinant++;}
        if (Determinant_aux[w]) {Determinant_aux[w] = 0;Euler_Determinant--;}
        else {Determinant_aux[w] = 1; Euler_Determinant++;}
    }

    void Determinant (std::ostream& out){
        if (Euler_Determinant==0){
            out << "CIRCLE";
        }else if ( Euler_Determinant==2)
        {
            int first=NULL;
            int last =NULL;
            for (int i=0; i<Number_Of_Vertices;i++){
                if(Determinant_aux[i]==1 && first==NULL){
                    first = i;
                } else if (Determinant_aux[i] ==1){
                    last = i;
                }
            }
            out << "PATH" << " " << first << " " << last;
        }else{
            out << "IMPOSSIBLE";
        }
    }
};

int main(){
    int v; int e;
    int u; int w;
    cin >> v >> e;
    Graph Graph1(v,e);
    for ( int i =0; i<e;i++){
        cin >> u >> w;
        Graph1.AddEdge(u,w);
    }
    Graph1.Determinant(cout);
}