#include <bits/stdc++.h>
using namespace std;
typedef long long int ll;
typedef long double ld;
#define pb push_back
#define pf push_front
#define fi first
#define se second
const ll mod = 1e9+7, mxn = 3e5+7;
ll n, a[mxn], k;
pair<ll,ll> lmb(ll x)
{
pair<ll,ll> dp[mxn][2];
dp[1][0] = {0,0}; dp[1][1] = {a[1]-x,1};
for (ll i = 2; i <= n; i++)
{
dp[i][0] = max(dp[i-1][0],dp[i-1][1]);
dp[i][1] = max(make_pair(dp[i-1][0].fi+a[i]-x,dp[i-1][0].se+1),
make_pair(dp[i-1][1].fi+a[i],dp[i-1][1].se));
}
return max(dp[n][0],dp[n][1]);
}
void aliens()
{
ll l = 0, r = 1e18, ans = -1;
while (r >= l)
{
ll m = (r+l)>>1;
pair<ll,ll> opt = lmb(m);
if (opt.se <= k)
{
ans = max(ans,opt.fi+m*opt.se);
r = m-1;
}
else l = m+1;
}
cout << ans;
}
signed main()
{
ios_base::sync_with_stdio(0); cin.tie(0); cout.tie(0);
// freopen("test.inp","r",stdin); freopen("test.out","w",stdout); freopen("test.err","w",stderr);
cin >> n >> k;
for (ll i = 1; i <= n; i++) cin >> a[i];
aliens();
}
