#include <iostream>
#include <cmath>
using namespace std;

int main() {
    
    int i, n;
    double *array;
    double sum = 0;
    
    cout << "Input size of array:" << endl;
    cin >> n;
    
    array = new double[n];
    
    cout << "Input elements of array:" << endl;
    for (i = 0; i < n; i++) {
        cin >> array[i];
    }
    
    for (i = 0; i < n; i++) {
        if (i % 2 == 0) {
            sum += array[i];
        }
    }
    
    cout << "sum = " << sum << endl;
    
    
    delete[] array;
    
    return 0;
}