#include <bits/stdc++.h>
#define int long long
#define pb push_back
#define fs first
#define sc second
using namespace std;
const int N = 100000;
int a[N], b[N], diff[N];
signed main() {
int n, k;
cin >> n >> k;
if(k >= n){
cout << n << endl;
return 0;
}
for(int i = 1; i <= n; i++){
cin >> a[i];
b[i] = a[i] + 1;
}
for(int i = 1; i < n; i++){
diff[i] = a[i + 1] - b[i];
}
sort(diff + 1, diff + n, greater<int>());
int cnt = 0, sum = 0;
while(k--){
sum += diff[cnt];
cnt++;
}
cout << b[n] - a[1] - sum;
}
