//desinged by Sadig Agayev
#include <bits/stdc++.h>
//#include <ext/pb_ds/assoc_container.hpp>
using namespace std;
//using namespace __gnu_pbds;
#define int long long
#define ull unsigned long long
#define fora for(int i=0;i<n;i++)
#define fors for(int i=0;i<s.size();i++)
#define forv for(int i=0;i<v.size();i++)
#define sorta sort(a,a+n)
#define sorts sort(s.begin(),s.end())
#define sortv sort(v.begin(),v.end())
#define reversea reverse(a,a+n)
#define reverses reverse(s.begin(),s.end())
#define reversev reverse(v.begin(),v.end())
#define proqueue priority_queue<long long, vector<long long>, greater<long long> >
#define mp makepair
#define mt make_tuple
#define hurryup ios_base::sync_with_stdio(0); cin.tie(0); cout.tie(0);
#define vv vector<vector<int>>
#define MAX 1e6
#define INF 1e9
#define EPS 1e-9
//typedef tree<int,null_type,greater<int>,rb_tree_tag, tree_order_statistics_node_update>indexed_set;;
//typedef tree<int, null_type, less_equal<int>, rb_tree_tag,tree_order_statistics_node_update>indexed_multiset;
signed main(){
int n,k;
cin>>n>>k;
vector<int>v(n);
fora cin>>v[i];
if(n == k){
cout<<k<<endl;
return 0;
}
if(k == 1){
cout<<(v[n-1]+1) - v[0]<<endl;
return 0;
}
}
