#pragma comment(linker, "/STACK:1024000000,1024000000")#include<cstdio>#include<cstring>#include<cmath>#include<algorithm>#include<vector>#include<map>#include<set>#include<queue>#include<stack>#include<ctime>#include<iostream>using namespace std;typedef long long LL;const double pi=acos(-1.0);void File(){    freopen("D:\\in.txt","r",stdin);    freopen("D:\\out.txt","w",stdout);}template <class T>inline void read(T &x){    char c = getchar();    x = 0;    while(!isdigit(c)) c = getchar();    while(isdigit(c))    {        x = x * 10 + c - ‘0‘;        c = getchar();    }}int n;int c[200010];int nc[200010];int u[200010];int v[200010];int belong[200010];int block;vector<int>G[200010];int flag[200010];vector<int>L[200010],R[200010];int ans;int a[200010];void dfs(int x){    belong[x]=block;    for(int i=0;i<G[x].size();i++)    {        int to=G[x][i];        if(c[to]!=c[x]) continue;        if(belong[to]!=0) continue;        dfs(to);    }}void dp(int x){    flag[x]=1;    int mx=0;    for(int i=0;i<G[x].size();i++)    {        int to=G[x][i];        if(flag[to])        {            L[x].push_back(mx);            continue;        }        dp(to);        mx=max(mx,a[to]);        L[x].push_back(mx+1);    }    a[x]=mx+1;}void dp2(int x){    flag[x]=1;    int mx=0;    for(int i=G[x].size()-1;i>=0;i--)    {        int to=G[x][i];        if(flag[to])        {            R[x].push_back(mx);            continue;        }        dp2(to);        mx=max(mx,a[to]);        R[x].push_back(mx+1);    }    a[x]=mx+1;}void Find(int x,int h){    flag[x]=1;    int nh;    int sz=G[x].size();    for(int i=0;i<G[x].size();i++)    {        int root=G[x][i];        if(flag[root]) continue;        nh=h+1;        int k=0;        if(i-1>=0) k=max(k,L[x][i-1]);        if(sz-i-2>=0) k=max(k,R[x][sz-i-2]);        if(k!=0) nh=max(nh,k+1);        ans=min(ans,max(nh,a[root]));        Find(root,nh);    }}int main(){    cin>>n;    for(int i=1;i<=n;i++) cin>>c[i];    for(int i=1;i<=n-1;i++)    {        cin>>u[i]>>v[i];        G[u[i]].push_back(v[i]);        G[v[i]].push_back(u[i]);    }    for(int i=1;i<=n;i++)    {        if(belong[i]!=0) continue;        block++; nc[block]=c[i]; dfs(i);    }    for(int i=1;i<=n;i++) G[i].clear();    for(int i=1;i<=n-1;i++)    {        if(c[u[i]]==c[v[i]]) continue;        G[belong[u[i]]].push_back(belong[v[i]]);        G[belong[v[i]]].push_back(belong[u[i]]);    }    memset(flag,0,sizeof flag); dp(1);    memset(flag,0,sizeof flag); dp2(1);    ans=a[1];    memset(flag,0,sizeof flag); Find(1,1);    printf("%d\n",ans-1);    return 0;}