#include<bits/stdc++.h> using namespace std; using ll = long long; void solve() { int n; cin>>n; int ct1=0, ct2=0, ct3=0, ct4=0; for(int i=0; i<n; ++i) { int x; cin>>x; if(x==1) ct1++; else if(x==2) ct2++; else if(x==3) ct3++; else ct4++; } int taxi=ct4; if(ct2>1) { taxi=taxi+ct2/2; ct2=ct2%2; } while(ct3>0 && ct1>0) { taxi++; ct3--; ct1--; } if(ct3>0) taxi=taxi+ct3; if(ct1>0 && ct2>0) { taxi++; ct2--; ct1=ct1-2; } while(ct2>0) { taxi++; ct2--; } while(ct1>0) { taxi++; ct1=ct1-4; } cout<<taxi<<endl; } int main() { ios_base::sync_with_stdio(false); cin.tie(nullptr); int TC = 1; //cin >> TC; //cin.ignore(); while (TC--) solve(); }