#include <iostream>
#include <vector>
#include <algorithm>
#include <cmath>
using namespace std;
 
bool f(double a, double b){ //Вспомогательная функция для сортировки вектора по убыванию
	return a>b;
}
 
int main() {
	vector<double> real;
	double value;
	while(cin >> value){
		real.push_back(value);
	}
	int size = real.size();
	int size_of_sum = ceil(size%2==0?size/2:size/2+1); //Размер вектора сумм
	vector<double> sum;
	for(int i = 0; i < size_of_sum; i++){
		if(i == size_of_sum-1 && size%2 != 0) sum.push_back(2*real[i]);// Средний элемент массива real при нечетном size
		else sum.push_back(real[i] + real[size - i - 1]);
	}
	sort(sum.begin(),sum.end(),f); // Сортировка по убыванию
	cout << sum[0];
	return 0;
}

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