#include <bits/stdc++.h>
#define F first
#define S second
#define X real()
#define Y imag()
using namespace std;
typedef long long ll;
typedef long double ld;
vector<pair<int, ll> > g[202020];
int u[202020];
int bc[202020];
int b[202020];
vector<int> fr[202020];
ll d[202020];
int main(){
ios_base::sync_with_stdio(0);
cin.tie(0);
int n,m,s;
cin>>n>>m>>s;
for (int i=0;i<m;i++){
int uu,v,w;
cin>>uu>>v>>w;
g[uu].push_back({v, w});
g[v].push_back({uu, w});
}
priority_queue<pair<ll, int> > dij;
d[s]=1;
dij.push({-1, s});
while (!dij.empty()){
auto xx=dij.top();
dij.pop();
int x=xx.S;
if (u[x]) continue;
u[x]=1;
int f=0;
for (int ex:fr[x]){
if (f==0){
f=bc[ex];
}
else if(f>0){
if (f!=bc[ex]){
f=-1;
}
}
}
if (f<=0){
bc[x]=x;
}
else{
bc[x]=f;
}
if (bc[x]==s) bc[x]=x;
if (bc[x]!=s) b[bc[x]]++;
for (auto nx:g[x]){
if (d[nx.F]==0||d[x]+nx.S<d[nx.F]){
d[nx.F]=d[x]+nx.S;
fr[nx.F].clear();
fr[nx.F].push_back(x);
dij.push({-d[nx.F], nx.F});
}
else if(d[x]+nx.S==d[nx.F]){
fr[nx.F].push_back(x);
}
}
}
int v=0;
for (int i=1;i<=n;i++){
v=max(v, b[i]);
}
cout<<v<<endl;
}
