#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
typedef pair<ll,ll> ii;
const int MAXN = 1e5 + 10;
ll vetor[MAXN],N,K;
ii dp[MAXN];
ii solve(ll W){
dp[0] = ii(0,0);
ii best = ii(-vetor[1] + 1,0);
for(ll i = 1;i<=N;i++){
dp[i] = ii(best.first + vetor[i] + W,best.second - 1);
best = min(best, ii(-vetor[i+1] + 1 + dp[i].first,dp[i].second) );
}
return dp[N];
}
int main(){
cin.tie(0);ios_base::sync_with_stdio(0);
cin >> N >> K;
for(ll i = 1;i<=N;i++) cin >> vetor[i];
ll ini = 0, fim = (ll)2*1e9, resp = -1,meio;
while(ini <= fim){
meio = (ini+fim)/2;
if(abs(solve(meio).second) >= K){
resp = meio;
ini = meio + 1;
}
else{
fim = meio - 1;
}
}
cout << solve(resp).first - K*resp << endl;
return 0;
}
