测试用例的意外输出

Codeforces问题158B-http://codeforces.com/problemset/problem/158/B

我得到了测试用例5的意外输出。我认为我应该得到1作为输出，但我是2。请指导我。法官日志：

测试：#5，时间：30ms，内存：380KB，退出代码：0，检查器退出代码：1，判决：WRONG_ANSWER输入2.2 1输出2.答复1.检查器日志应为错误答案1，找到2

我的解决方案：

#include<iostream>
using namespace std;
int n,a[100000],i,b,c,d,e,f,g,h;
int main()
{
    cin>>n;
    for(i=0;i<n;i++)
    {
        cin>>a[i];
    }
    b=0;
    c=0;
    d=0;
    e=0;
    for(i=0;i<n;i++)
    {
        if(a[i]==1) //To check for number of 1,2,3 and 4 membered groups.
        b=b+1;
        if(a[i]==2)
        c=c+1;
        if(a[i]==3)
        d=d+1;
        if(a[i]==4)
        e=e+1;  
    }
    f=e;
    if(d>b) //More 3 member groups than 1.
    {
        f=f+d; //f=f+b+(g-b) 3 and 1 member groups combine.Remaining 3 i.e. (g-b) member groups will can't combine with 2 member groups.Hence,they take separate taxies.
        g=-1;
    }
    if(b>=d) //More 1 member groups than 3.
    {
        f=f+d;
        g=b-d; //g=remaining 1 member groups.
    }
    h=(2*c)%4; //Empty seats in last taxi.Possible values can be 0,1,2,3.
    if(h==0)
    f=f+(c/2);
    else
    f=f+((c+1)/2);
    if(g!=-1)
    {
        g=g-h; //Remaining 1 member groups after combining with remaining seats in last 2 member taxi.
        if((g%4)==0)
        f=f+(g/4);
        else
        f=f+(g/4)+1;
    }
    cout<<f;
}