#include <bits/stdc++.h>
using namespace std;
#define ll long long
#define ld long double
void solve(){
int N, K; cin >> N >> K; K--;
int bef, first, answer;
vector<int> len;
cin >> bef; first = bef;
for(int i = 2; i <= N; ++i){
int cur; cin >> cur;
len.push_back(cur - bef - 1);
bef = cur;
answer = cur - first + 1;
}
if(N == 1){
cout << 1;
return;
}
sort(len.rbegin(), len.rend());
for(int i = 0; i < K; ++i){
answer -= len[i];
}
cout << answer;
}
int main(){
ios_base::sync_with_stdio(0); cin.tie(0); cout.tie(0);
int tc = 1; //cin >> tc;
while(tc--){
solve();
}
return 0;
}
