//g++ -o sol sol.cpp
//cd C:\Users\Asus-1\OneDrive\Desktop
#include <bits/stdc++.h>
using namespace std;
#define ld long double
#define int long long
const int INF = 1e18;
const int mod=1e9+7;
#define S(a) a.begin(),a.end()
#define pb push_back
#define READ(l , r , a) for(int i = l;i <= r;i++) cin >> a[i]
#define printV(l , r , a) for(int i = l;i <= r;i++) cout << a[i] << ' ';
#define pii pair < int , int >
#define FOR(i , l , r) for(int i = l;i <= r;i++)
#define mp make_pair
void solve(){
int n,k;
cin>>n>>k;
--k;
vector<int>a(n);
for(int &i:a) cin>>i;
vector<int>all;
for(int i=0;i<n-1;i++) all.pb(a[i+1]-a[i]);
sort(all.rbegin(),all.rend());
int res=a[n-1]-a[0]+1;
for(int i=0;i<k;i++) res-=(all[i]-1);
cout<<res<<endl;
}
signed main(){
ios_base::sync_with_stdio();
cin.tie(0);
cout.tie(0);
int T=1;//cin>>T;
while(T--) solve();
}
