export {};

const input: string[] = require("fs").readFileSync(0, "utf8").toString().trim().split('\n')
let link = Array.from({length : Number(input[0])+1}, () => []);
let visited = new Array(Number(input[0])+1).fill(false);
input.slice(2).forEach(v => {
    const [a,b] = v.split(" ").map(Number);
    link[a].push(b);
    link[b].push(a);
});

const dfs = (now: number) => {
    visited[now] = true;
    for(let nt of link[now]){
        if(!visited[nt]){
            dfs(nt);
        }
    }
}

dfs(1);
let count: number = 0;
visited.forEach((v)=>{if(v) count++;});
console.log(count-1);