#include <bits/stdc++.h>
#define int long long
#define fi first
#define pll pair<long long, long long>
#define se second
#define isz(a) (int)a.size()
using namespace std;
const long long inf = 1e18;
const int maxn = 1e5 + 5;
const int mod = 1e9 + 7;
int n, k;
int a[maxn];
void subfull(){
priority_queue<int> pq;
for (int i = 2; i <= n; ++i) pq.push(a[i] - a[i - 1]);
int ans = a[n] - a[1] + 1;
int cnt = 1;
while (cnt < k){
int x = pq.top();
pq.pop();
ans -= x - 1;
++cnt;
}
cout << ans;
}
void solve(){
cin >> n >> k;
for (int i = 1; i <= n; ++i) cin >> a[i];
subfull();
}
signed main(){
ios_base::sync_with_stdio(0);
cin.tie(0); cout.tie(0);
int t = 1; // cin >> t;
while (t--){
solve();
}
}
