#pragma GCC optimize("Ofast,unroll-loops")
#include <bits/stdc++.h>
#define int long long
#define ll long long
#define down cout<<'\n';
#define debug cout<<" cucuucucuuu",down
#define modwwe int t;cin>>t; while(t--)
#define bit(i,j) (i>>j&1)https://loj.ac/s/2349245
#define sobit(a) __builtin_popcountll(a)
#define task2 "top1apio"
#define task "test"
#define fin(x) freopen(x".inp","r",stdin)
#define fou(x) freopen(x".out","w",stdout)
#define pb push_back
#define mask(k) (1ll<<k)
#define checktime cerr << (double)clock() / CLOCKS_PER_SEC * 1000 << " ms";
using namespace std;
#define getchar_unlocked getchar
mt19937 rd(chrono::steady_clock::now().time_since_epoch().count());
using i128 = __int128;
int rand(int l, int r)
{
return uniform_int_distribution<int>(l, r)(rd);
}
void phongbeo();
const int inf = 1e9;
const int mod2 = 998244353;
//const ll base=67;
int n, m, s1, s2, s4, s3, sf, k, s5, s6, s7, s8, s9, mx2, res, dem2 = 0, dem = 0, s33, dem3, dem4, mid, l2,
r2, center;
int i, s10, s12, k1, k2, k3, s11, lim, w, l, r, dem5, dem6, dem7, dem9, now, root, q, en;
int el = 19;
main()
{
///top1apio
if (fopen(task2".inp", "r"))
{
fin(task2);
fou(task2);
}
///top1apio
if (fopen(task".inp", "r"))
{
fin(task);
fou(task);
}
///top1apio
ios_base::sync_with_stdio(0);
cout.tie(0);
cin.tie(0);
// cin>>s1;
//ll t;cin >> t;while (t--)
phongbeo();
/// checktime
///top1apio
}
int dp[500001][2][2][2];
int c[2][2][2];
string s;
int sz[500001];
vector<int> v[500001];
void dfs(int x,int y)
{
for(auto f:v[x])
if(f^y)
{
dfs(f,x);
sz[x]+=sz[f];
}
int state=s[x-1]-'0';
dp[x][state][0][0]=0;
dp[x][1-state][0][1]=1;
sz[x]+=state;
for(auto f:v[x])
if(f^y)
{
for(int i=0; i<=1; i++)
for(int j=0; j<=1; j++)
for(int t=0; t<=1; t++)
{
///i color x
///j color f
///case1:no root
for(int g=0; g<=1; g++)
{
if(j==1)c[1-i][t][g]=min(c[1-i][t][g],dp[x][i][t][g]+dp[f][j][0][0]+2);
else
{
if(dp[f][j][0][0]==0)c[i][t][g]=min(dp[x][i][t][g],c[i][t][g]);
else c[i][t][g]=min(dp[x][i][t][g]+dp[f][j][0][0]+4,c[i][t][g]);
}
}
///case 2: root and no root but
if(t==0)
{
for(int g=0; g<=1; g++)
{
if(j==1)c[i][1][g]=min(c[i][1][g],dp[x][i][t][g]+dp[f][j][1][0]+1);
else
{
c[1-i][1][g]=min(dp[x][i][t][g]+dp[f][j][1][0]+3,c[1-i][1][g]);
}
}
}
///case3: root on f
for(int g=0; g<=1-t; g++)
{
if(g==0)
{
if(j==1)
{
c[i][t][1]=min(c[i][t][1],dp[x][i][t][0]+dp[f][j][g][1]+3);
}
else
{
c[1-i][t][1]=min(c[1-i][t][1],dp[x][i][t][0]+dp[f][j][g][1]+1);
}
}
else
{
if(j==1)
{
c[1-i][g][1]=min(c[1-i][g][1],dp[x][i][t][0]+dp[f][j][g][1]+2);
}
else
{
c[i][g][1]=min(c[i][g][1],dp[x][i][t][0]+dp[f][j][g][1]+4);
}
}
}
}
for(int i=0; i<=1; i++)
for(int j=0; j<=1; j++)
for(int t=0; t<=1; t++)
{
dp[x][i][j][t]=c[i][j][t];
c[i][j][t]=inf;
}
}
for(int i=0; i<=1; i++)
{
dp[x][i][1][1]=min(dp[x][i][0][1],dp[x][i][1][1]);
dp[x][i][1][0]=min(dp[x][i][0][0],dp[x][i][1][0]);
}
if(sz[x]==dem)
{
s4=min(s4,dp[x][0][1][1]);
}
}
void phongbeo()
{
cin>>n>>s;
for(int i=1; i<n; i++)
cin>>l>>r,v[l].pb(r),v[r].pb(l);
for(int i=1; i<=n; i++)
for(int j=0; j<2; j++)
for(int z=0; z<2; z++)
for(int t=0; t<2; t++){
dp[i][j][z][t]=inf;
c[j][z][t]=inf;
}
for(int i=0; i<n; i++)
if(s[i]=='0')s[i]='1',dem++;
else s[i]='0';
s4=inf;
dfs(1,0);
cout<<s4;
}
