#include <stdio.h>
#include <string.h>
#include <limits.h>
#define MAXN 310
struct tnode {int num;tnode *next;
} g[MAXN],*t;
int q[MAXN * 3],list[MAXN],loc[MAXN],dist[MAXN],from[MAXN],dis[MAXN],di[MAXN][MAXN],xdis[MAXN][MAXN];
int n,l,r,s,x,y,z,tot,ans;
bool v[MAXN],in_tree[MAXN];
void insert(int x,tnode &p) {t = new(tnode);t->num = x;t->next = p.next;p.next = t;
}
void dfs(int father,int x) {tnode *tt;tt = g[x].next;while (tt != NULL) {int y = tt->num;if (!in_tree[y])if (dist[x] + di[x][y] < dist[y]) {dist[y] = dist[x] + di[x][y];from[y] = father;dfs(father,y);}tt = tt->next;}
}
int main() { scanf("%d%d",&n,&s);for (int i = 1;i < n;++i) {scanf("%d%d%d",&x,&y,&z);insert(x,g[y]);insert(y,g[x]);di[x][y] = z;di[y][x] = z;}q[0] = 1;v[1] = 1;while (l <= r) {x = q[l];t = g[x].next;while (t != NULL) {y = t->num;if (y != from[x])if (dis[y] < di[x][y] + dis[x]) {dis[y] = di[x][y] + dis[x];from[y] = x;if (!v[y]) {q[++r] = y;v[y] = 1;}}t = t->next;}++l;v[x] = 0;}z = 0;for (int i = 1;i <= n;++i)if (dis[i] > z) {z = dis[i];x = i;}memset(from,0,sizeof(from));memset(v,0,sizeof(v));v[x] = 1;memset(dis,0,sizeof(dis));q[0] = x;v[x] = 1;l = r = 0;while (l <= r) {x = q[l];t = g[x].next;while (t != NULL) {y = t->num;if (from[x] != y)if (dis[y] < di[x][y] + dis[x]) {dis[y] = di[x][y] + dis[x];from[y] = x;if (!v[y]) {q[++r] = y;v[y] = 1;}}t = t->next;}++l;v[x] = 0;}z = 0;for (int i = 1;i <= n;++i)if (dis[i] > z) {z = dis[i];x = i;}list[++tot] = x;while (from[x]) {x = from[x];list[++tot] = x;}for (int i = 1;i <= tot;++i) {loc[list[i]] = i;in_tree[list[i]] = 1;}for (int i = 1;i <= tot;++i)for (int j = i + 1;j <= tot;++j)xdis[i][j] = xdis[i][j - 1] + di[list[j - 1]][list[j]];memset(from,0,sizeof(from));for (int i = 1;i <= n;++i)if (!in_tree[i])dist[i] = INT_MAX;for (int i = 1;i <= tot;++i)dfs(list[i],list[i]);ans = INT_MAX;for (int st = 1;st <= tot;++st)for (int en = st;en <= tot;++en) {if (xdis[st][en] > s)break;int te_ans = 0;for (int i = 1;i <= n;++i)if (!in_tree[i]) {if (dist[i] > te_ans)te_ans = dist[i];} else {x = loc[i];if (x < st) {if (dist[i] + xdis[x][st] > te_ans)te_ans = dist[i] + xdis[x][st];}if (x > en) {if (dist[i] + xdis[en][x] > te_ans)te_ans = dist[i] + xdis[en][x];}}if (te_ans < ans)ans = te_ans;}printf("%d\n",ans);return 0;
}