#include<bits/stdc++.h>
using namespace std;
#define all(fl) fl.begin(),fl.end()
#define pb push_back
#define fi first
#define se second
#define for1(i,j,k) for(int i=j;i<=k;i++)
#define for2(i,j,k) for(int i=j;i>=k;i--)
#define for3(i,j,k,l) for(int i=j;i<=k;i+=l)
#define lb lower_bound
#define ub upper_bound
#define sz(a) (int)a.size()
#define pii pair<int,int>
#define pli pair<long long,int>
#define gcd __gcd
#define lcm(x,y) x*y/__gcd(x,y)
#define pil pair<int,long long>
long long a[100009];
signed main(){
ios_base::sync_with_stdio(0);
cin.tie(0);
//freopen("temp.INP","r",stdin);
//freopen("temp.OUT","w",stdout);
int n,k;
cin>>n>>k;
priority_queue<long long>t;
for1(i,1,n)cin>>a[i];
k--;
for1(i,2,n){
t.push(a[i]-a[i-1]-1);
}
long long sum=a[n]+1-a[1];
while (k--&&!t.empty()){
sum-=t.top();
t.pop();
}
cout<<sum;
}
