#include <bits/stdc++.h>

using namespace std;

int n;

const int maxN = 55;
int v[maxN][2];
int votes_left[maxN];
int potential_votes[maxN];

bool backtrack(int idx, int monster){
    if(idx == n+1) return true;
    if(idx == monster || v[idx][0] == monster || v[idx][0] == monster) return backtrack(idx+1,monster);

    for (int t = 0; t < 2; t++) {
        if (votes_left[v[idx][t]] >= potential_votes[v[idx][t]]) {
            potential_votes[v[idx][0]]--;
            potential_votes[v[idx][1]]--;
            votes_left[v[idx][t]]--;
            if (backtrack(idx + 1, monster)) return true;
            potential_votes[v[idx][0]]++;
            potential_votes[v[idx][1]]++;
            votes_left[v[idx][t]]++;
            return false;
        }
    }

    potential_votes[v[idx][0]]--;
    potential_votes[v[idx][1]]--;
    for (int t = 0; t < 2; t++) {
        if (votes_left[v[idx][t]] == 0) continue;
        votes_left[v[idx][t]]--;
        if (backtrack(idx + 1, monster)) return true;
        votes_left[v[idx][t]]++;
    }
    potential_votes[v[idx][0]]--;
    potential_votes[v[idx][1]]--;
    return false;
}

void solve() {

    cin >> n;

    for(int i = 1;i <= n; i++){
        cin >> v[i][0] >> v[i][1];
    }

    int ans = 0;
    for(int i = 1; i <= n; i++){

        for(int j = 1; j <= n; j++){
            canBeVoted[j] = 0;
            potential_votes[j] = 0;
        }

        for(int j = 1; j <= n; j++){
            if(v[j][0] == i || v[j][1] == i){
                potential_votes[i]++;
                continue;
            }else{
                potential_votes[v[j][0]]++;
                potential_votes[v[j][1]]++;
            }

        }

        if((n+2)/3 + 3 < potential_votes[i])
            continue;
        if (potential_votes[i] < 2) {
            ans++;
            continue;
        }

        for(int j = 1; j <= n; j++){
            if(j == i)
                continue;
            votes_left[j] = potential_votes[i] - 1;
        }
        votes_left[v[i][0]]--;
        votes_left[v[i][1]]--;

        if(!backtrack(1,i)){
            ans++;
        }
    }
    cout << ans << "\n";
}

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

    solve();

    return 0;
}