#include<bits/stdc++.h>
using namespace std;
#define rep(i,a,n) for(int i=a;i<n;i++)
#define per(i,a,n) for(int i=n-1;i>=a;i--)
#define fi first
#define se second 
#define ll long long
#define pb push_back
typedef pair<long long,long long> pll;
typedef pair<int,int> pii;
typedef vector<int> vi;
typedef vector<long long> vll;
typedef double db;
const ll mod=1e9+7;
ll powmod(ll a,ll b,ll p){ll res=1;a%=p;while(b){if(b&1) res=res*a%p;a=a*a%p;b>>=1;}return res;}
ll gcd(ll a,ll b) {return b?gcd(b,a%b):a;}
int _;
const int N = 2e6+10;
int sum;
int n;
char s[N];
int pe[N];
int main(){
    for(scanf("%d",&_);_;_--){
        sum=0;
        scanf("%d",&n);
        scanf("%s",s+1);
        int ans=0;
        rep(i,1,n+1){
            if(s[i] == '0') {
                if(sum) { ans++;sum--;}
            }
            else if(s[i] == '1'){
                sum++;
            } 
            else if(s[i] == '2') ans++;
            else ans++;
        }
        ans+=sum/2;
        
        printf("%d\n",ans);
    }
}

 

</details>