#include<bits/stdc++.h>
#define pb push_back
#define fi first
#define se second
//#define TimeCalculation
using namespace std;
const int N = 1e5 + 1;
int n, k;
int t[N];
priority_queue<int> pq;
int main(){
ios_base::sync_with_stdio(0);
cin.tie(0);
cout.tie(0);
#ifdef TimeCalculation
auto starttime = chrono::high_resolution_clock::now();
#endif
cin >> n >> k;
for(int i = 1; i <= n; ++i){
cin >> t[i];
if(i > 1){
pq.push(t[i] - t[i - 1] - 1);
}
}
int ans = t[n] + 1 - t[1];
--k;
while(k--){
ans -= pq.top();
pq.pop();
}
cout << ans;
#ifdef TimeCalculation
auto endtime = chrono::high_resolution_clock::now();
auto duration = chrono::duration_cast<chrono::milliseconds>(endtime - starttime).count();
cout << "\n=====" << "\nTime elapsed: " << duration << " ms\n";
#endif
}
