#include<bits/stdc++.h>
#define fi first
#define se second
#define ll long long
#define pii pair<ll,ll>
#define el '\n'
#define file(name) if (fopen(name".inp", "r")) { freopen(name".inp", "r", stdin); freopen(name".out", "w", stdout); }
#define N 100006
using namespace std;
ll T[N];
int n, k;
pii cal(int m){
ll cnt = 0, res = 0, pre = T[1];
for (int i = 1; i <= n + 1; i++){
if (T[i] + 1 - pre > m) {
res += T[i - 1] - pre + 1;
cnt++;
pre = T[i];
}
}
return {cnt, res};
}
int main()
{
ios_base::sync_with_stdio(0); cin.tie(0); cout.tie(0);
cin >> n >> k;
for (int i = 1; i <= n; i++){
cin >> T[i];
}
T[n + 1] = 1e9 + 2;
ll l = 1, r = T[n] + 1, res = 1e9;
while(l <= r){
ll m = (l + r)/2;
pii c = cal(m);
if (c.fi <= k){
res = min(res, c.se);
r = m - 1;
}
else l = m + 1;
}
cout << res;
return 0;
}
