#include<bits/stdc++.h>
using namespace std;
using ll = long long;
using pii = pair<int,int>;
const int N = 1e6+10;
int t,n,m,k,l,r,op,x,y,u,v;
int f[N];
unordered_map<int,vector<int>>mp;
bool vis[N];
bool flag;
struct nd{
    int v;
    int l;
};
queue<nd> q;
void solve(){
    cin>>n>>m;
    q.push({m,0});
    vis[m] = true;
    for(int i = 1;i<=n-1;i++){
        cin>>u>>v;
        mp[u].push_back(v);
        mp[v].push_back(u);
    }
    while(!q.empty()){
        auto [t,l] = q.front();
        q.pop();
//      cout<<t<<" "<<l<<"\n";
        for(int num:mp[t]){
            if(vis[num])continue;
            q.push({num,l+1});
            vis[num] = true;
        }
        if(q.empty()){
            cout<<l<<"\n";
            return ;
        }
    }
}
int main(){
    ios::sync_with_stdio(false);
    cin.tie(nullptr);
    cout.tie(nullptr);  
    solve();
    return 0;
}