#include <bits/stdc++.h>

#define rep(i,n) for(long long int (i)=0;(i)<(int)(n);(i)++)
#define rrep(i,a,b) for(long long int i=(a);i<(b);i++)
#define rrrep(i,a,b) for(long long int i=(a);i>=(b);i--)
#define all(v) (v).begin(), (v).end()
#define pb(q) push_back(q)
#define Abs(a,b) max(a,b)-min(a,b)
#define YES(condition) if(condition){cout << "YES" << endl;}else{cout << "NO" << endl;}
#define Yes(condition) if(condition){cout << "Yes" << endl;}else{cout << "No" << endl;}
#define Cout(x) cout<<(x)<<endl
#define POSSIBLE(n) cout << ((n) ? "POSSIBLE" : "IMPOSSIBLE"  ) << endl
#define Possible(n) cout << ((n) ? "Possible" : "Impossible"  ) << endl
#define possible(n) cout << ((n) ? "possible" : "impossible"  ) << endl
#define Size(n) (n).size()

typedef long long ll;
//typedef pair<int,int> P;

using namespace std;

const int INF = 1e9,MOD = 1e9 + 7;
const ll LINF = 1e18;

/*---------------------------------------------------------------
long long int kaizyo(long long int hh){
    cmp=1;
    while(hh>1){
        cmp=(cmp*hh)%MOD;
        hh--;
    }
    return cmp;
}
long long int ruizyo(long long int aa, long long int bb){
    if(aa==0){
        return 1;
    }
    else if(aa%2==0){
        long long int tt=ruizyo(aa/2,bb);
        return (tt*tt)%MOD;
    }
    else{
        return (ruizyo(aa-1,bb)*bb)%MOD;
    }
}フェルマ－のア
---------------------------------------------------------------

while(x!=0){
            sum+=x%10;
          / x/=10;
        }
        各桁の和
---------------------------------------------------------------

pair<int,int> p[100000];
cin >> tmp;
p[i]=make_pair(tmp,i);
cout << p[i].second+1 << endl;//ペアの右側つまりiを出力
---------------------------------------------------------------

s.find(w[i])==string::npos
findの使い方
---------------------------------------------------------------

for(int i=0;i<n;i++){
    b[i]=x%2;
    x/=2;
  }二進数
---------------------------------------------------------------

bool f[100001];//1000000以下の素数を調べよう！
rrep(i,2,100001){
       f[i]=false;
    }
rrep(i,2,100001){
        if(!f[i]){
            for(int j=i+i;j<=100000;j+=i){
                f[j]=true;
            }
        }
    }
    for(int i=3;i<=100000;i+=2){
        if(!f[i]){
            c[i]++;
        }
    }
---------------------------------------------------------------

visited=vector<vector<bool>>(10,vector<bool>(10,false));アを全部falseに
---------------------------------------------------------------

long long gcd(long long aaa,long long bbb){
    if(bbb==0){
        return aaa;
    }
    return gcd(bbb,aaa%bbb);
}
 
long long lcm(long long aaa,long long bbb){
    long long g = gcd(aaa,bbb);
    return aaa/g * bbb;
}左から最大公約数と最小公倍数


---------------------------------------------------------------

long long int prime_cnt[10000];
       for(int i=2;i*i<=n;i++){
           while(n%i==0){
               n/=i;
               prime_cnt[i]+=1;
           }
           if(n>1){
               prime_cnt[n]+=1;
               break;
           }
      }ある数nを素因数分解しましょう
---------------------------------------------------------------*/

 int n,cnt=0,ans=0,a,b,c,d[1000000],cmp,cmpp,m,h,w,x,y,sum=0,pos;
int dy[]={1,0,-1,0};
int dx[]={0,1,0,-1};
string alph("abcdefghijklmnopqrstuvwxyz"),s;
bool fl=true;
struct edge{int to,cost;};
vector<edge> g[1000000];

//-------------------------↓↓↓↓↓↓------------------------
void dijkstra(int s){
        priority_queue<pair<int,int>,vector<pair<int,int>>,greater<pair<int,int>>>que;
        fill(d,d+n,INF);
        d[s]=0;
        que.push(pair<int,int>(0,s));
        while(!que.empty()){
            pair<int,int> p=que.top();que.pop();
            int v=p.second;
            if(d[v]<p.first)continue;
            rep(i,Size(g[v])){
                edge e=g[v][i];
                if(d[e.to]>d[v]+e.cost){
                    d[e.to]=d[v]+e.cost;
                    que.push(pair<int,int>(d[e.to],e.to));
                }
            }
        }
}

int main(void){
       cin.tie(0);
    ios::sync_with_stdio(false);

       cin >> n >> m;
       rep(i,m){
           cin>>a>>b;
           a--;b--;
           g[a].push_back({b,1});
           g[b].push_back({a,1});
       }
       dijkstra(0);
       POSSIBLE(d[n-1]==2);
       
return 0;
}


Measured memory_bytes: 34152