BOJ-2606

#include <iostream>
#include <vector>

using namespace std;

vector<int> virus[101];
bool check[101];

int dfs_count(int x) {
    int count=0;
    check[x] = true;
    for (int i=0; i<virus[x].size(); i++) {
	int y = virus[x][i];
	if (!check[y]) {
	    dfs_count(y);
	    count++;
	}
    }
    return count;
}

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

    int n, m;
    cin >> n >> m;
    for (int i=0; i<m; i++) {
	int u, v;
	cin >> u >> v;
	virus[u].push_back(v);
	virus[v].push_back(u);
    }
    int ans = dfs_count(1);
    cout << ans << endl;
}