#include <iostream>
#include <cstdio>
#include <string>
#include <algorithm>
#include <vector>
#include <sstream>
#include <queue>
using namespace std;
const int maxn = 1e6;
long long a[maxn+5];
long long n,k;
priority_queue<long long> q;
void solve()
{
cin >> n >> k;
k--;
for(int i = 1; i <= n; i++)
cin >> a[i];
long long ans = a[n] - a[1] + 1;
for(int i = 2; i <= n; i++)
q.push(a[i]-a[i-1]-1);
while(k--)
ans -= q.top(), q.pop();
cout << ans;
}
int main()
{
ios_base::sync_with_stdio(false);
cin.tie(NULL);
cout.tie(NULL);
solve();
return 0;
}
