// LUOGU_RID: 98796908
#include<bits/stdc++.h>
using namespace std;
const int MAXN=2e5+1,INF=1e9;
int n,a[MAXN];
inline int cost1() {
	//a[i] and a[i+1]
	int ret=INF;
	for(int i=1;i<n;++i) {
		if(max(a[i],a[i+1])>=2*min(a[i],a[i+1])) ret=min(ret,(max(a[i],a[i+1])+1)/2);
		else ret=min(ret,(a[i]+a[i+1]+2)/3);
	}
	return ret;
}
inline int cost2() {
	//a[i-1] and a[i+1]
	int ret=INF;
	for(int i=2;i<n;++i) {
		ret=min(ret,(a[i-1]+a[i+1]+1)/2);
	}
	return ret;
}
inline int cost3() {
	//a[x] and a[y], |x-y|>2
	int fir=INF,sec=INF;
	for(int i=1;i<=n;++i) {
		if(a[i]<fir) sec=fir,fir=a[i];
		else if(a[i]<sec) sec=a[i];
	}
	return (fir+1)/2+(sec+1)/2;
}
signed main() {
	scanf("%d",&n);
	for(int i=1;i<=n;++i) scanf("%d",&a[i]);
	printf("%d\n",min(min(cost1(),cost2()),cost3()));
	return 0;
}