//Jay Shree Krishna

#include"bits/stdc++.h"
#define fast ios_base::sync_with_stdio(false); cin.tie(NULL); cout.tie(NULL)
#define ll long long int
#define inf 1e18+5
#define sr string
#define M 1000000007
#define start int t;cin>>t;while(t--)
#define db(x) cout<<#x<<"="<<x<<"\n"
#define db2(a,b)cout<<#a<<": "<<a<<" , "<<#b<<": "<<b<< endl;
#define db3(a,b,c)cout<<#a<<": "<<a<<" , "<<#b<<": "<<b<<" , "<<#c<<": "<<c<<endl;
#define forr(i, n) for (int i = 0; i < n; i++)
#define fr(i, n) for (int i = 1; i <= n; i++)
#define rep(i,j,k) for(int i = j; i < k; i++)
#define rp(i,j,k) for(int i = j; i <=k; i++)
#define nn "\n"
#define en "\n"
#define vvi vector<vector<int>>
#define vi vector<int>
#define si set<int>
#define mlsi multiset<int>
#define vc vector<char>
#define vli vector<long long int>
#define vpii vector<pair<ll,ll>>
#define pii pair<ll,ll>
#define mii map<ll,ll>
#define msi map<string,int>
#define mci map<char,int>
#define umii unordered_map<int,int>
#define umsi unordered_map<string,int>
#define umci unordered_map<char,int>
#define mkp make_pair
#define pb push_back
#define eb emplace_back
#define all(x) x.begin(),x.end()
#define sortv(x) sort(x.begin(),x.end())
#define sorta(x,n) sort(x,x+n)
#define sorted(x) is_sorted(x.begin(),x.end())
#define print_all(x) for(auto t:x) cout<<t<<" ";cout<<en;
#define mxe(x) *max_element(all(x))
#define mne(x) *min_element(all(x))
#define ub upper_bound
#define lb lower_bound
#define go(x) for(auto &[u,v]:x)
#define in(x) cin>>x
#define in2(x,y) cin>>x>>y
#define in3(x,y,z) cin>>x>>y>>z
#define in4(x,y,z,v) cin>>x>>y>>z>>v
#define oo(x) cout<<x<<en
#define oo2(x,y) cout<<x<<" "<<y<<en
#define oo3(x,y,z) cout<<x<<" "<<y<<" "<<z<<en
#define ood(n,x) cout<<fixed<<setprecision(n)<<x<<"\n"
#define sz(x) x.size()
#define ff first
#define ss second
#define ooy cout<<"Yes\n"
#define oon cout<<"No\n"
#define ooyy cout<<"YES\n"
#define oonn cout<<"NO\n" 
#define rr return
#define cc continue

using namespace std;

template<class T> bool ckmin(T &a, const T &b) { return a > b ? a = b, 1 : 0; }
template<class T> bool ckmax(T &a, const T &b) { return a < b ? a = b, 1 : 0; }
 
void read(vli &a,int n){
    a.resize(n);
    forr(i,n) cin>>a[i];
}

bool fine=0;
vli a,b;
ll n,m;
const int N=1e5+9;
vi adj[N];
vi vis(N);

void solve(){
    in2(n,m);
    int u,v;
    vi edges;
    forr(i,m){
        cin>>u>>v;
        u--;v--;
        adj[u].pb(v);
        adj[v].pb(u);
        edges.pb(u);
        edges.pb(v);
    }
    ll ans=0;
    forr(i,n){
        //int x=edges[i];
        if(!vis[i]){
            queue<int> q;
            q.push(i);
            while(q.size()){
                int curr=q.front();
                vis[curr]=1;
                q.pop();
                for(auto v:adj[curr]){
                    if(!vis[v]) q.push(v);
                }
            }
            ans++;
        }
    }
    oo(ans-1);
}

int main(){
   #ifndef ONLINE_JUDGE 
    freopen("input1.txt", "r", stdin); 
    freopen("error.txt", "w", stderr); 
    freopen("output1.txt", "w", stdout); 
    #endif
    fast;
    if(fine){
        start{
            solve();
        }
   }
   else solve();
    return 0;
}


Measured memory_bytes: 9712