Codeforces158B.c

#include<stdio.h>
int main()
{
    int c1=0,c2=0,c3=0,c4=0,sum=0,x,n,i;
    scanf("%d",&n);
    for(i=0;i<n;i++){
        scanf("%d",&x);
        if(x==1) c1++;
        else if(x==2) c2++;
        else if(x==3) c3++;
         else c4++;
    }
    sum+=c4;
    c4=0;
    sum+=c2/2;
    c2=c2%2;
    if(c1>=c3){
        sum+=c3;
        c1=c1-c3;
        c3=0;
        sum+=c1/4;
        c1=c1%4;

    if(c1+c2*2<=4 && c1+c2*2>0){
        sum++;
        c1=0;
        c2=0;
    }
    else if (c1==3 && c2==1){
        sum+=2;
        c1=0;
        c2=0;
    }
    }
    else if(c1<c3){
        sum+=c1;
        c3=c3-c1;
        c1=0;
        sum+=c3+c2;
    }
    printf("%d\n",sum);
        }