> #include <iostream>
> #include <stdio.h>
> using namespace std;
> 
> int adjQuList[1010][1010];
> int adjQuDist[1010][1010];
> int adjQuNum[1010] = {0};
> int adjFeiList[1010][1010];
> int adjFeiDist[1010][1010];
> int adjFeiNum[1010] = {0};
> 
> int main() {
> 	int N, M, X;
> 	scanf("%d%d%d", &N, &M, &X);
> 	for(int i = 0; i < M; i++){
> 		int from, to, dist;
> 		scanf("%d%d%d", &from, &to, &dist);
> 		adjQuList[from][adjQuNum[from]] = to;
> 		adjQuDist[from][adjQuNum[from]] = dist;
> 		adjQuNum[from]++;
> 		adjFeiList[to][adjFeiNum[to]] = from;
> 		adjFeiDist[to][adjFeiNum[to]] = dist;
> 		adjFeiNum[to]++;
> 	}
> 	int quDist[1010], feiDist[1010];
> 	for(int i = 1; i <= N; i++){
> 		quDist[i] = 1000000000;
> 	}
> 	for(int j = 1; j <= N; j++){
> 		feiDist[j] = 1000000000;
> 	}
> 	quDist[X] = feiDist[X] = 0;
> 	bool quUsed[1010] = {0}, feiUsed[1010] = {0};
> 	for(int i = 1; i <= N; i++){
> 		int mn = 2147483647, arg = -1;
> 		for(int j = 1; j <= N; j++){
> 			if(quUsed[j]) continue;
> 			if(quDist[j] < mn){
> 				mn = quDist[j];
> 				arg = j;
> 			}
> 		}
> 		quUsed[arg] = 1;
> 		for(int j = 0; j < adjQuNum[arg]; j++){
> 			if(quUsed[adjQuList[arg][j]]) continue;
> 			int newDist = quDist[arg] + adjQuDist[arg][j];
> 			if(newDist < quDist[adjQuList[arg][j]]){
> 				quDist[adjQuList[arg][j]] = newDist;
> 			}
> 		}
> 	}
> 	for(int i = 1; i <= N; i++){
> 		int mn = 2147483647, arg = -1;
> 		for(int j = 1; j <= N; j++){
> 			if(feiUsed[j]) continue;
> 			if(feiDist[j] < mn){
> 				mn = feiDist[j];
> 				arg = j;
> 			}
> 		}
> 		feiUsed[arg] = 1;
> 		for(int j = 0; j < adjFeiNum[arg]; j++){
> 			if(feiUsed[adjFeiList[arg][j]]) continue;
> 			int newDist = feiDist[arg] + adjFeiDist[arg][j];
> 			if(newDist < feiDist[adjFeiList[arg][j]]){
> 				feiDist[adjFeiList[arg][j]] = newDist;
> 			}
> 		}
> 	}
> 	int mx = 0;
> 	for(int i = 1; i <= N; i++){
> 		int tmp = quDist[i] + feiDist[i];
> 		if(tmp > mx) mx = tmp;
> 	}
> 	printf("%d\n", mx);
> 	return 0;
> }