#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
const int  mx= 100000;
int dp[mx];
bool vis[mx];
int arr[mx];
int n,k;
int solve(int i)
{
    if (i >= n)
        return 0;
    if (vis[i])
        return dp[i];
    vis[i] = 1;
    dp[i] = max(solve(i + 1),arr[i] + solve(i + 2));
    return dp[i];
}
int main()
{
    cin>>n>>k;
    for(int i=0;i<n;i++)
        cin>>arr[i];
    cout << solve(0)<<endl;
}