#include <bits/stdc++.h>
using namespace std;
bool isend = 0, vis[100010];
int fa[100010], numd, numb;
int find(int x) {
    if(x == fa[x]) return x;
    return fa[x] = find(fa[x]);
}
void solve() {
    memset(vis, 0, sizeof(vis));
    for(int i = 1; i <= 100000; i++) fa[i] = i;
    bool f = 0;
    numd = 0, numb = 0;
    while(1) {
        int u, v;
        cin >> u >> v;
        if(u == 0 && v == 0) break;
        if(u == -1 && v == -1) {
            isend = 1;
            return;
        }
        numb++;
        if(fa[u] == fa[v]) f = 1;
        else fa[u] = v;
        if(!vis[u]) {
            vis[u] = 1;
            numd++;
        }
        if(!vis[v]) {
            vis[v] = 1;
            numd++;
        }
        if(f) {
            cout << 0 << '\n';
            return;
        }
        //cout << numd << ' ' << numb << '\n';
    }
    if(numd - 1 == numb) cout << 1 << '\n';
    else cout << 0 << '\n';
}
int main() {
    while(1) {
        solve();
        if(isend) return 0;
    }
}