#include <iostream>
#include <cstdio>
#include <algorithm>
#include <cmath>
#include <vector>
#include <list>
#include <set>
#include <map>
#include <queue>
#include <stack>
#include <cctype>
#include <cassert>
#include <climits>
#include <string>
#include <bitset>
#include <cfloat>
#include <random>
#include <iomanip>
#include <unordered_set>
using namespace std;
typedef long double ld;
typedef long long int ll;
typedef unsigned long long int ull;
typedef vector<int> vi;
typedef vector<char> vc;
typedef vector<bool> vb;
typedef vector<double> vd;
typedef vector<string> vs;
typedef vector<ll> vll;
typedef vector<pair<int,int> > vpii;
typedef vector<pair<ll,ll> > vpll;
typedef vector<vi> vvi;
typedef vector<vvi> vvvi;
typedef vector<vc> vvc;
typedef vector<vs> vvs;
typedef vector<vll> vvll;
typedef map<int,int> mii;
typedef set<int> si;
#define rep(i,n) for(ll i = 0; i < (n); ++i)
#define rrep(i,n) for(int i = 1; i <= (n); ++i)
#define arep(i,v) for(auto i : v)
#define irep(it, stl) for(auto it = stl.begin(); it != stl.end(); it++)
#define drep(i,n) for(int i = (n) - 1; i >= 0; --i)
#define fin(ans) cout << (ans) << '\n'
#define STLL(s) strtoll(s.c_str(), NULL, 10)
#define mp(p,q) make_pair(p, q)
#define pb(n) push_back(n)
#define all(a) a.begin(), a.end()
#define rall(a) a.rbegin(), a.rend()
#define Sort(a) sort(a.begin(), a.end())
#define Rort(a) sort(a.rbegin(), a.rend())
#define MATHPI acos(-1)
#define fi first
#define se second
constexpr int dx[8] = {1, 0, -1, 0, 1, -1, -1, 1};
constexpr int dy[8] = {0, 1, 0, -1, 1, 1, -1, -1};
template <class T> inline bool chmax(T& a,T b){if(a<b){a=b;return 1;} return 0;}
template <class T> inline bool chmin(T& a,T b){if(a>b){a=b;return 1;} return 0;}
template <class T> inline void dump(T &v){irep(i, v){cout<<*i<<((i==--v.end())?'\n':' ');}}
inline string getline(){string s; getline(cin,s); return s;}
inline void yn(const bool b){b?fin("yes"):fin("no");}
inline void Yn(const bool b){b?fin("Yes"):fin("No");}
inline void YN(const bool b){b?fin("YES"):fin("NO");}
struct io{io(){ios::sync_with_stdio(false);cin.tie(0);}};
const int INF = INT_MAX;
constexpr ll LLINF = 1LL<<60;
constexpr ll MOD = 1000000007;
constexpr ld EPS = 1e-11;

template <typename T>
class WAR_FLY {
public:
    vector<vector<T>> d; // 辺の数
    int V; // 頂点の数
    
    WAR_FLY(int n) {
        V = n;
        d = vector<vector<T> > (n,vector<T>(n));
        for(int i = 0; i < V; i++) {
            for(int j = 0; j < V; j++) {
                if(i == j) {
                    d[i][j] = 0;
                }
                else {
                    d[i][j] = LLINF;
                }
            }
        }
    }

    void warshall_floyd(void) {
        for(int k = 0; k < V; k++) {
            for(int i = 0; i < V; i++) {
                for(int j = 0; j < V; j++) {
                    d[i][j] = min((ll)d[i][j], (ll)d[i][k] + (ll)d[k][j]);
                }
            }
        }
    }

    void add(int from, int to, T cost) {
        d[from][to] = cost;
    }

    bool is_negative_loop(void) {
        for(int i = 0; i < V; i++) {
            if(d[i][i] < 0) return true;
        }
        return false;
    }

    void show(void) {
        for(int i = 0; i < V; i++) {
            for(int j = 0; j < V; j++) {
                cout << d[i][j] << " ";
            }
            cout << endl;
        }
    }
};

int main() {
    
    int n,m;
    cin>>n>>m;
    WAR_FLY<ll> wa(n);
    rep(i,m){
        int s,t;
        cin>>s>>t;
        wa.add(s,t,-1);
    }
    wa.warshall_floyd();
    int ans=wa.is_negative_loop();
    fin(ans);
}


Measured memory_bytes: 3244