S_maxim

#include <bits/stdc++.h>

using namespace std;
ifstream fin("smax.in");
ofstream fout("smax.out");

int n, a[100005];
long long max(long long a, long long b)
{
	return (a > b) ? a : b;
}

long long FindMaxSum(int arr[], int n)
{
	long long incl = 0;
	long long excl = 0;
	long long old_incl = 0;
	int i = 0;

	while (i < n)
	{
		old_incl = incl;
		incl = max(old_incl, excl + 0LL + arr[i]);
		excl = old_incl;
		i++;
	}

	return incl;
}
int main()
{
    fin>>n;
    for(int i=0; i<n; i++)
        fin>>a[i];
    fout<<FindMaxSum(a,n);
    return 0;
}