https://ac.nowcoder.com/acm/contest/332/D

C++版本一

题解：

从前往后，如果偶数那就自己两个两个取

如果奇数那就和后面一个分别取一个一次，然后自己两个两个取

如果奇数，后面的不存在那就两个两个，留下一个剩下来

/*
*@Author:   STZG
*@Language: C++
*/
#include <bits/stdc++.h>
#include<iostream>
#include<algorithm>
#include<cstdlib>
#include<cstring>
#include<cstdio>
#include<string>
#include<vector>
#include<bitset>
#include<queue>
#include<deque>
#include<stack>
#include<cmath>
#include<list>
#include<map>
#include<set>
//#define DEBUG
#define RI register int
using namespace std;
typedef long long ll;
//typedef __int128 lll;
const int N=100000+10;
const int MOD=1e9+7;
const double PI = acos(-1.0);
const double EXP = 1E-8;
const int INF = 0x3f3f3f3f;
int t,n,m,k,q;
ll ans,cnt,flag,temp;
int a[N];
char str;
int main()
{
#ifdef DEBUG
	freopen("input.in", "r", stdin);
	//freopen("output.out", "w", stdout);
#endif
    scanf("%d",&n);
    //scanf("%d",&t);
    //while(t--){}
    for(int i=1;i<=n;i++)
        scanf("%d",&a[i]);
    for(int i=1;i<=n;i++){
        if(a[i]%2==0){
            ans+=a[i]/2;
        }else{
            if(a[i+1]>0){
                a[i+1]--;
                ans+=(a[i]+1)/2;
            }else{
                ans+=a[i]/2;
            }
        }
    }
    cout << ans << endl;
    //cout << "Hello world!" << endl;
    return 0;
}