Submission #1030720

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Source Code Expand

#include <algorithm>
#include <cassert>
#include <cfloat>
#include <climits>
#include <cmath>
#include <cstdio>
#include <cstdlib>
#include <deque>
#include <iomanip>
#include <iostream>
#include <limits>
#include <map>
#include <queue>
#include <set>
#include <sstream>
#include <stack>
#include <string>
#include <vector>

#define FOR(i,k,n) for (int (i)=(k); (i)<(n); ++(i))
#define rep(i,n) FOR(i,0,n)
#define pb push_back
#define eb emplace_back
#define mp make_pair
#define fst first
#define snd second
#define all(v) begin(v), end(v)
#define debug(x) cerr<< #x <<": "<<x<<endl
#define debug2(x,y) cerr<< #x <<": "<< x <<", "<< #y <<": "<< y <<endl

using namespace std;
typedef long long ll;
typedef unsigned long long ull;
typedef pair<int, int> pii;
typedef vector<int> vi;
typedef vector<vector<int> > vvi;
typedef vector<ll> vll;
typedef vector<vector<ll> > vvll;
template<class T> using vv=vector<vector< T > >;

int main() {
  int n;
  scanf("%d", &n);
  vi a;
  a.reserve(n);
  vi g(5, 0);
  rep (i, n) {
    int tmp;
    scanf("%d", &tmp);
    g[tmp] += 1;
  }
  int ans = 0;
  ans += g[4];
  ans += g[3];
  int g1 = max(0, g[1] - g[3]);
  ans += (g[2] / 2);
  int g2 = g[2] % 2;
  ans += (2 * g2 + g1 + 3) / 4;
  printf("%d\n", ans);
  return 0;
}

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