#include<bits/stdc++.h>
#define ll long long
#define endl "\n"
#define fi first
#define se second
#define pb push_back
#define pll pair<long long, long long>
#define loop(i,n) for(int i=1;i<=n;i++)
#define loop0(i,n) for(int i=0;i<n;i++)
using namespace std;
//pbds template
//#include <ext/pb_ds/assoc_container.hpp>
//#include <ext/pb_ds/tree_policy.hpp>
//using namespace __gnu_pbds;
//template <class T>
//using ordered_set = tree<T, null_type, less<T>, rb_tree_tag,tree_order_statistics_node_update>;
void solve(){
ll n,k;
cin >> n >> k;
priority_queue<ll> pq;
ll prev = -1;
ll first = -1;
for(int i=1;i<=n;i++){
ll a;
cin >> a;
if(prev!=-1) pq.push((a-prev));
if(first == -1) first = a;
prev = a;
}
// cout << "DEBUG" << endl;
ll ans = prev-first+1;
ll turn = k-1;
while(turn>0){
ans -= pq.top()-1;
pq.pop();
turn--;
}
cout << ans << endl;
}
int main(){
// ios::sync_with_stdio(false);
// cin.tie(0);
// cout.tie(0);
int tc = 1;
// cin >> tc;
while(tc--){
solve();
}
}
