#include <bits/stdc++.h>
#define ll long long
#define fast1 ios_base::sync_with_stdio(false);cin.tie(NULL);cout.tie(NULL);
#define endl "\n"
using namespace std;
#pragma GCC optimize("Ofast")
#pragma GCC target("fma,sse,sse2,sse3")
#pragma GCC optimize("unroll-loops")
int t,n,k;
int dizi[100005];
int dp[100005][5];
vector<pair<int,int> > v;
void solve()
{
cin>>n>>k;
for(int i=1;i<=n;i++)
cin>>dizi[i];
for(int i=1;i<n;i++)
v.push_back({dizi[i+1]-dizi[i]-1,i});
sort(v.begin(),v.end());
reverse(v.begin(),v.end());
int cevap=dizi[n]+1-dizi[1];
for(int i=0;i<k-1;i++)
cevap-=v[i].first;
cout<<cevap;
}
int main()
{
fast1
//freopen ("myfile.gir","r",stdin);
//freopen ("myfile.cik","w",stdout);
t=1;
//cin>>t;
while(t--)
solve();
return 0;
}
