#include <bits/stdc++.h>
using namespace std;
long long n,k,a[300001];
void read()
{
cin>>n>>k;
for(long long i=1;i<=n;i++)
cin>>a[i];
}
pair<long long,long long> dp[300001][2];
pair<long long,long long> group(long long x)
{
dp[1][0]={0,0};
dp[1][1]={a[1]-x,1};
for(long long i=2;i<=n;i++)
{
dp[i][0]=max(dp[i-1][0],dp[i-1][1]);
pair<long long,long long> p1={dp[i-1][0].first+a[i]-x,dp[i-1][0].second+1},
p2={dp[i-1][1].first+a[i],dp[i-1][1].second};
dp[i][1]=max(p1,p2);
//cout<<dp[i][0].first<<" "<<dp[i][1].first<<" "<<dp[i][1].second<<" "<<dp[i][0].second<<endl;
}
return max(dp[n][0],dp[n][1]);
}
void solve()
{
long long ans=0;
long long l=0,r=1e18;
while(l<=r)
{
long long m=(l+r)/2;
pair<long long,long long> g=group(m);
if(g.second>=k)
{
//cout<<"in "<<m<<" "<<g.first<<" "<<g.second<<endl;
ans=g.first+m*k;
l=m+1;
}
else r=m-1;
}
cout<<ans<<endl;
}
int main()
{
ios_base::sync_with_stdio(false);
cin.tie(NULL);
cout.tie(NULL);
read();
solve();
return 0;
}
/*
10 4
2 0 1 1 0 1 1 1 1 1
*/
