#include <bits/stdc++.h>
using namespace std;
template <class T>
void debug(T a, T b) {
  for (; a != b; ++a) cerr << *a << ' ';
  cerr << endl;
}
template <class T>
void chmin(T& a, const T& b) {
  if (a > b) a = b;
}
template <class T>
void chmax(T& a, const T& b) {
  if (a < b) a = b;
}
namespace std {
template <class S, class T>
ostream& operator<<(ostream& out, const pair<S, T>& a) {
  out << '(' << a.first << ',' << a.second << ')';
  return out;
}
}  // namespace std
bool valid[200005];
struct DomTree {
  static const int MAX_V = 200000;
  int semi[MAX_V], U[MAX_V], idom[MAX_V];
  int puf[MAX_V], par[MAX_V];
  int mn[MAX_V];
  void init() {
    memset(puf, -1, sizeof(puf));
    for (int i = 0; i < (MAX_V); ++i) mn[i] = i;
  }
  int root(int a) {
    if (puf[a] == -1) return a;
    int r = root(puf[a]);
    if (semi[mn[puf[a]]] < semi[mn[a]]) mn[a] = mn[puf[a]];
    return puf[a] = r;
  }
  void unite(int a, int b) { puf[b] = a; }
  int eval(int v) {
    root(v);
    return mn[v];
  }
  int cnt;
  int vs[MAX_V];
  vector<int> bucket[MAX_V];
  vector<int> g[MAX_V], rg[MAX_V];
  void dfs(int v) {
    semi[v] = cnt;
    vs[cnt++] = v;
    for (int u : g[v])
      if (semi[u] < 0) {
        par[u] = v;
        dfs(u);
      }
  }
  vector<int> g3[200005];
  int size[200005];
  int dfs3(int v) {
    if (valid[v]) size[v] = 1;
    for (auto to : g3[v]) {
      size[v] += dfs3(to);
    }
    return size[v];
  }
  int solve(int n, int r, vector<int>* g_) {
    init();
    for (int i = 0; i < (n); ++i) {
      g[i] = g_[i];
      rg[i].clear();
    }
    for (int i = 0; i < (n); ++i)
      for (auto to : g[i]) {
        rg[to].push_back(i);
      }
    for (int i = 0; i < (n); ++i) semi[i] = -1;
    cnt = 0;
    dfs(r);
    for (int i = n - 1; i > 0; i--) {
      int w = vs[i];
      for (int v : rg[w]) {
        int u = eval(v);
        chmin(semi[w], semi[u]);
      }
      bucket[vs[semi[w]]].push_back(w);
      for (int v : bucket[par[w]]) U[v] = eval(v);
      bucket[par[w]].clear();
      unite(par[w], w);
    }
    for (int i = 1; i < n; i++) {
      int w = vs[i];
      int u = U[w];
      if (semi[w] == semi[u])
        idom[w] = semi[w];
      else
        idom[w] = idom[u];
    }
    for (int i = 1; i < n; i++) {
      int w = vs[i];
      idom[w] = vs[idom[w]];
    }
    idom[r] = -1;
    for (int i = 0; i < (n); ++i)
      if (i != r) g3[idom[i]].push_back(i);
    dfs3(r);
    int res = 0;
    for (int i = 0; i < (n); ++i)
      if (i != r) chmax(res, size[i]);
    return res;
  }
};
DomTree D;
int n, m, s;
vector<pair<int, int> > g[200005];
const long long int INF = 1e18;
long long int cost[200005];
vector<int> g2[200005];
int main() {
  cin >> n >> m >> s;
  --s;
  for (int i = 0; i < (m); ++i) {
    int a, b, c;
    scanf("%d%d%d", &a, &b, &c);
    --a;
    --b;
    g[a].push_back({b, c});
    g[b].push_back({a, c});
  }
  for (int i = 0; i < (n); ++i) cost[i] = INF;
  priority_queue<pair<long long int, int>, vector<pair<long long int, int> >,
                 greater<pair<long long int, int> > >
      pq;
  pq.push({0, s});
  cost[s] = 0;
  while (!pq.empty()) {
    pair<long long int, int> cur = pq.top();
    pq.pop();
    if (cost[cur.second] < cur.first) continue;
    for (auto e : g[cur.second]) {
      if (cost[e.first] > cur.first + e.second) {
        cost[e.first] = cur.first + e.second;
        pq.push({cost[e.first], e.first});
      }
    }
  }
  for (int i = 0; i < (n); ++i)
    if (cost[i] < INF)
      for (auto e : g[i]) {
        if (cost[e.first] == cost[i] + e.second) g2[i].push_back(e.first);
      }
  for (int i = 0; i < (n); ++i)
    if (cost[i] < INF) valid[i] = 1;
  for (int i = 0; i < (n); ++i)
    if (cost[i] == INF) g2[s].push_back(i);
  int res = D.solve(n, s, g2);
  cout << res << endl;
  return 0;
}
