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#include<iostream>
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using namespace std;
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int main()
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{
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   int n;cin>>n;
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   int one=0,two=0,three=0,four=0;
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   for(int i=0;i<n;i++) {
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      int x;cin>>x;
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      if(x==1)
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         one++;
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      else if(x==2)
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         two++;
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      else if(x==3)
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         three++;
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      else
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         four++;
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   }
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   int ans=0;
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   ans+=four;
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   ans+=three;
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   one-=three;
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   if(two%2==0) {
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      //even
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      ans+=two/2;
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   }
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   else {
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      //odd
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      ans+=two/2 +1;
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      one-=2;
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   }
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   //1 2 3
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   if(one>0)
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      ans+=(one+3)/4;
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   cout<<ans<<'\n';
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}