#include<bits/stdc++.h>
using namespace std;
#define fi first
#define se second
#define lowbit(x) ((x)&(-x))
#define ll long long
const int N=1005;
int a[N]; 
int main(){
	ios::sync_with_stdio(0),cin.tie(0),cout.tie(0);
	int n;
	cin>>n;
	for(int i=1;i<=n;i++)
	cin>>a[i];
	int dj=0,yh=0,xz=0; //能量，永恒，心之
	for(int i=1;i<=n;i++){ 
		if(yh==1){
			yh=0;
		    xz++;	
		}
		dj+=a[i];
		if(dj<6) continue;
		if(dj/6%2||i==n){
			yh+=dj/6;
			xz+=yh/2;
			dj%=6;
			yh%=2;
		}
		else{
			yh+=(dj-6)/6;
			xz+=yh/2;
			dj=6;
			yh%=2;
		}
	}
	cout<<xz;
}