#include<iostream>
#include<cstring>
#include<sstream>
#include<cstdio>
#include<algorithm>
#include<queue>
using namespace std;
#define read(x) scanf("%lld",&x)
#define Read(x,y) scanf("%lld%lld",&x,&y)
#define gc(x) scanf(" %c",&x)
#define mmt(x,y) memset(x,y,sizeof x)
#define write(x) printf("%d
",x)
#define INF 0x3f3f3f3f
#define ll long long
#define mod ((1LL<<31) - 1LL)
const ll N = 3e5+5;
const ll M = 1e6;
ll d[N];
bool vis[N];
ll head[N],tot;
ll p[N];
struct Edge
{
ll next;
ll to;
ll dis;
}edge[N*2];
inline void add(ll from,ll to,ll dis)
{
edge[++tot].next = head[from];
edge[tot].to = to;
edge[tot].dis = dis;
head[from] = tot;
}
struct node
{
ll id,val;
node(){}
node(ll a,ll b):id(a),val(b){}
bool operator <(node A)const{
return val > A.val;
}
};
void dij(ll u)
{
mmt(p,0x7f);
mmt(d,0x7f);
mmt(vis,0);
d[u] = 0;
p[u] = 0;
priority_queue<node> Q;
Q.push({u,0});
node tmp;
while(Q.size()){
tmp = Q.top();
Q.pop();
int x = tmp.id;
if(vis[x]) continue;
vis[x] = 1;
for(int i = head[x];~i;i = edge[i].next){
int y = edge[i].to;
ll dis = edge[i].dis;
if(d[y] >= d[x] + dis){
p[y] = min(p[y],dis);
d[y] = d[x] +dis;
Q.push({y,d[y]});
}
}
}
}
void init()
{
mmt(head,-1);
tot = 0;
}
int main()
{
init();
ll n,m;
ll f,t,dis;
Read(n,m);
for(ll i = 1;i <= m;++i){
Read(f,t);read(dis);
add(f,t,dis);
add(t,f,dis);
}
read(t);
dij(t);
ll ans = 0;
for(int i = 1;i <= n;++i){
ans += p[i];
}
cout<<ans<<endl;
}