#include<bits/stdc++.h>
using namespace std;

#define IOS std::cin.tie(0);std::ios_base::sync_with_stdio(false)

#define ll      long long
#define Fi      first
#define Se      second
#define Pb      push_back
#define vi      vector<int>
#define vp      vector<pair<int,int>>
#define vvi     vector<vector<int>>
#define vvp     vector<vector<pair<int,int>>>

#define sz(x) (int)x.size()
#define all(v) v.begin(),v.end()
#define output_s(s) printf("%s\n",(s).c_str())
#define END cout<<"\n"

#define rep(i,n)        for(int i=0;i<(int)(n);i++)
#define Rep(i,n,m)      for(int i=(int)(n);i<(int)(m);i++)
#define RepS(i,n,m)     for(int i=(int)(n);i<=(int)(m);i++)
#define RRepS(i,n,m)    for(int i=(int)(n);i>=(int)(m);i--)
#define SRepS(i,n,m)    for(int i=(int)(n);i*i<=(int)(m);i++)
#define RepA(x)         for(auto &item:(x))

void CINT(){} //@shibh308's template
template<class Head,class... Tail> void CINT(Head&& head,Tail&&... tail){cin>>head; CINT(move(tail)...);}    
#define CIN(...) int __VA_ARGS__;CINT(__VA_ARGS__)
#define LCIN(...) ll __VA_ARGS__;CINT(__VA_ARGS__)
#define SCIN(...) string __VA_ARGS__;CINT(__VA_ARGS__)
#define VCIN(x) for(auto &item:x) cin>>item

void OUT(){}
template<class Head,class...Tail> void OUT(Head&& head,Tail&&...tail){cout<<head<<(sizeof...(tail)?" ":"\n"); OUT(move(tail)...);}
#define COUT(...) OUT(__VA_ARGS__)

template<typename TypeInt>TypeInt GCD(TypeInt a,TypeInt b){return a%b==0?b:GCD(b,a%b);} //Greatest Common Divisor
template<typename TypeInt>TypeInt LCM(TypeInt a,TypeInt b){return a*b/GCD(a,b);} //Least Common Multiple
template<class T>inline bool chmax(T &a,const T &b){if(a<b){a=b;return true;}return false;}
template<class T>inline bool chmin(T &a,const T &b){if(b<a){a=b;return true;}return false;}
template<class T>bool comp(T a,T b){return abs(a)<abs(b);} //比較関数

void YES(bool f){printf(f?"YES\n":"NO\n");}
void Yes(bool f){printf(f?"Yes\n":"No\n");}
void Possible(bool f){printf(f?"Possible\n":"Impossible\n");}
void POSSIBLE(bool f){printf(f?"POSSIBLE\n":"IMPOSSIBLE\n");}

//---------------------Template------------------------//

//Prime Factorization
//The result is stored in the array
void PrimeFactorize(long long num,vector<long long> &ret){
    vector<long long> prime(num+1,0);
    vector<long long>::iterator it;
    while(num%2==0){
        num /= 2;
        prime[2]++;
    }
    for(int i=3;i<=num;i++){
        while(num%i==0){
            num /= i;
            prime[i]++;
        }
    }
    copy(prime.begin(),prime.end(),back_inserter(ret));
}

//Judge the prime number
bool IsPrime(int x){
    if(x<2) return false;
    else if(x==2) return true;
    else if(x%2==0) return false;
    for(int i=3;i*i<=x;i+=2){
        if(x%i==0)return false;
    }
    return true;
}

//Meguru binary search
//left < right
template<typename T>class BinarySearch{
    T _l;
    T _r;
    function<bool(T)> _f;
    public:
        BinarySearch(T left,T right,function<bool(T)>func){
            this->_l=left;
            this->_r=right;
            this->_f=func;
        }
        ~BinarySearch() = default;
        T calc(){
            while((this->_r-this->_l)>1){
                T middle=(this->_l+this->_r)/2;
                if(this->_f(middle)){
                    this->_r=middle;
                }else{
                    this->_l=middle;
                }
            }
            return this->_r;
        }
};

//Dijkstra
template<typename T>class Dijkstra{
    T v; //vertex
    struct edge{
        T to;
        T cost;
    };
    const T INF=1e9;

    public:
    vector<vector<edge>> Graph;
    vector<T> dist;

    Dijkstra(T _v):Graph(v),dist(v,INF){
        this->v=_v;
    };
    virtual ~Dijkstra(){
        vector<vector<edge>>().swap(Graph);
    };
    /**
     * @param _f    from
     * @param _t    to
     * @param _c    cost (default = 1)
    */
    void addEdge(T _f, T _t, T _c = 1){
        Graph[_f].push_back(edge{_t,_c});
    }
    /**
     * @param _f Start position
     * @param _t Destination
    */
    T shortestPath(T _f,T _t){
        priority_queue<pair<T,T>,vector<pair<T,T>>,greater<pair<T,T>>> que;

        que.push(make_pair(0,_f));
        dist[_f]=0;

        while(!que.empty()){
            T v=que.top().second;
            que.pop();
            
            for(int i=0;i<Graph[v].size();i++){
                edge e=Graph[v][i];
                if(dist[e.to]>dist[v]+e.cost){
                    dist[e.to]=dist[v]+e.cost;
                    que.push(make_pair(dist[e.to],e.to));
                }
            }
        }
        return dist[_t];
    }
};

//----------------------Library------------------------//

const int dx4[]={1,0,-1,0}, dx8[]={1,0,-1,0,1,-1,-1,1};
const int dy4[]={0,1,0,-1}, dy8[]={0,1,0,-1,1,1,-1,-1};
const int NMAX = 55;
const int INF = 1e9;
const long long LINF = 1e18;
const double EPS = 1e-10;
const int MOD = 1e9+7;
bool flag = false;

//----------------------Global-------------------------//

//ダイクストラ法で解く
//初心者なのでどうしてこんなにメモリが大きくなるのかさっぱりわからない泣
signed main(){
    LCIN(N,M);
    Dijkstra<int> g(N);
    rep(i,M){
        CIN(a,b);
        a--;b--;
        g.addEdge(a,b);
        g.addEdge(b,a);
    }
    POSSIBLE(g.shortestPath(0,N-1)==2);
    
    return 0;
}

Measured memory_bytes: 124520