#include<iostream>
using namespace std;
int main()
{
	int size;
	cout<<"Enter the size of the array: ";
	cin>>size;

	double *arr = new double[size]; // creating a dymanic array of size "size"
	cout<<"Enter the array:"<<endl;
	for(int i=0;i<size;i++)
		cin>>arr[i]; //dynamically allocated arrays can be used like regular arrays

	double sum=0;
	for(int i=0; i<size; i+=2)
	{
		sum = sum + arr[i];
		if(i+1 < size) //in case size is odd
			sum = sum -arr[i+1];
	}

	cout<<"The sum is "<<sum<<endl;
	
	delete arr;
	return 0;
}