#include<bits/stdc++.h>
#include<ext/pb_ds/assoc_container.hpp>
/**zagaro & lauren <3**/
#define mod 1000000007 //1e9 + 7
#define pi acos(-1)
#define wl while
#define str string
#define ENDL "\n"
#define sal ' '
#define tp_set ll
#define prc(n) cout.precision(n);cout<<fixed;
#define ord_set tree<tp_set, null_type, less<tp_set>, rb_tree_tag, tree_order_statistics_node_update>
typedef long long ll;
typedef bool bl;
typedef char car;
using namespace std;
using namespace __gnu_pbds;
int main(){
ios_base::sync_with_stdio(0);
cin.tie(0); cout.tie(0);
ll n, k, a, b;
cin>>n>>k;
k = n-k;
cin>>a;
vector<ll> vec;
for(int i=2;i<=n;i++){
cin>>b;
vec.push_back(b-(a+1));
a=b;
}
sort(vec.begin(), vec.end());
for(int i=1;i<=k;i++)n+=vec[i-1];
cout<<n<<ENDL;
return 0;
}
