Codeforces VK Cup 2012 Qualification Round 1, problem: (B) Taxi solution

Codeforces  VK Cup 2012 Qualification Round 1, problem: (B) Taxi: http://codeforces.com/problemset/problem/158/B

Codeforces  VK Cup 2012 Qualification Round 1, problem: (B) Taxi solution: http://ideone.com/M7gmFE

#include <iostream>
#include <cstdio>
using namespace std;

int main() {
    int n, s, a[5]={0}, r;
    r=0;
    scanf("%d", &n);
    while(n--) scanf("%d", &s), a[s]++;
    r=a[4]+a[3];
    a[1]-=a[3];
    r+=a[2]*2/4;
    if(a[2]%2==1) {
        r++;
        a[1]-=2;
    } 
    if(a[1]>0) {
        r+=a[1]/4;
        if(a[1]%4>0) r++;
    }
    printf("%d", r);
    return 0;
} 

note: if taxi doesnt contain more than 4 or eqauls to 4 then you can increment passenger number