#include <iostream>
#include <vector>
#include <queue>
using namespace  std;
struct node {
    int index,najmal_pat;

    node(int s,int p){
        index = s;
        najmal_pat = p;
    }
    bool operator  < (const node&tmp) const {
        return najmal_pat > tmp.najmal_pat;
    }
};
int main() {
    int n,v;
    cin >> n >> v;
    vector<int> graph[15];
    int niza[n];
    for (int i = 0; i < n; i++) {
        cin >> niza[i];
        graph[niza[i]].push_back(i);
    }

    priority_queue<node> pq;
    vector<bool> visited (n+1, false);
    vector<bool> portali(15, false);
    pq.push(node(0,0));
    while(!pq.empty()){
        node current = pq.top();
        pq.pop();

        visited[current.index] = true;
        if(current.index == n-1){
            cout << current.najmal_pat;
            break;
        }
        if(!portali[niza[current.index]]) {
            for (int i = 0; i < graph[niza[current.index]].size(); i++) {
                int sosed = graph[niza[current.index]][i];
                int pat = current.najmal_pat + v;
                if(!visited[sosed])
                    pq.push(node(sosed, pat));
            }
            portali[niza[current.index]] = true;
        }

        if(current.index > 0 and !visited[current.index - 1]){
            pq.push(node(current.index -1,current.najmal_pat +1));

        }
        if(current.index < n and !visited[current.index + 1]){
            pq.push(node(current.index +1,current.najmal_pat+1));
        }
    }

}