#include <bits/stdc++.h>
using namespace std;
# define int long long
# define fir first
# define sec second
# define pb push_back
const int cnst = 2e5+5;
bool mutipletestcase = 0;
//bool debug = false;
void solve() {
int n, k; cin >> n >> k;
int num[n+5];
int ans = n;
priority_queue<int, vector<int>, greater<int>> pq;
for(int i = 1; i<=n; i++) {
cin >> num[i];
if(i != 1) pq.push(num[i]-num[i-1]-1);
}
int need = n-k;
while(need--) {
ans += pq.top();
pq.pop();
}
cout << ans << endl;
}
signed main() {
ios_base::sync_with_stdio(false);
int t = 1;
if(mutipletestcase) cin >> t;
while(t--) solve();
}
