// #pragma GCC optimize("O3,unroll-loops")
// #pragma GCC target("avx2,fma,bmi2,popcnt,lzcnt")
#include <bits/stdc++.h>
#define int long long
using namespace std;
mt19937_64 rnd(chrono::high_resolution_clock::now().time_since_epoch().count());
const int N=1e5;
int n,k,a[N+5];
void Solve(){
cin>>n>>k;
for (int i=1;i<=n;++i) cin>>a[i];
vector <int> v;
for (int i=1;i<n;++i) v.push_back(a[i+1]-a[i]-1);
sort(v.begin(),v.end(),greater<int>());
int ans=a[n]-a[1]+1;
for (int i=1;i<k;++i) ans-=v[i-1];
cout<<ans;
}
signed main(){
ios_base::sync_with_stdio(false);
cin.tie(NULL);
// freopen ("FILE.INP","r",stdin);
// freopen ("FILE.OUT","w",stdout);
int t=1;
while (t--) Solve();
cerr<<"\nTIME: "<<1000*clock()/CLOCKS_PER_SEC<<"ms\n";
}
