#[allow(dead_code)]
#[allow(unused_imports)]
fn read<T: std::str::FromStr>() -> T {
    use std::io::*;
    let stdin = stdin();
    let stdin = stdin.lock();
    let token: String = stdin
        .bytes()
        .map(|c| c.expect("failed to read char") as char)
        .skip_while(|c| c.is_whitespace())
        .take_while(|c| !c.is_whitespace())
        .collect();
    token.parse().ok().expect("failed to parse token")
}
use std::mem::*;
struct UnionFind {
    par: Vec<i64>,
}
#[allow(dead_code)] 
impl UnionFind {

    pub fn new(n: usize) -> Self {
        let par = (0..n).map(|_| -1).collect();
        Self{par}
    }

    pub fn root(&mut self, x: usize) -> i64 {
        if self.par[x] < 0{
            x as i64
        }else{
            self.par[x] = self.root(self.par[x] as usize);
            self.par[x]
        }
    }

    pub fn same(&mut self, x: usize, y: usize) -> bool {
        self.root(x) == self.root(y)
    }

    pub fn merge(&mut self, x: usize, y: usize) -> bool {
        let mut _x: i64 = self.root(x);
        let mut _y: i64 = self.root(y);
        if _x == _y {
            return false;
        }
        if self.par[_x as usize] > self.par[_y as usize] {
            swap(&mut _x, &mut _y);
        }
        self.par[_x as usize] += self.par[_y as usize];
        self.par[_y as usize] = _x as i64;
        return true;
    }
    pub fn size(&mut self, x: usize) -> i64 {
        (self.par[x]) as i64 * -1
    }
}
fn main(){
    let n:usize = read();
    let m:usize = read();
    let bc:Vec<(usize,usize)> = (0..n).map(|_| (read(),read())).collect();
    let mut rec = vec![Vec::new();n];
    let mut uf = UnionFind::new(m);
    for i in 0..n {
        rec[bc[i].1 - 1].push(bc[i].0 - 1);
    }
    let mut ans = 0;
    for i in 0..n {
        if rec[i].len() == 0 {
            continue;
        }
        let key = rec[i][0];
        for j in 0..rec[i].len() {
            if !uf.same(key,rec[i][j]) {
                ans += 1;
                uf.merge(key,rec[i][j]);
            }
        }
    }
    println!("{}",ans);
}