#include<bits/stdc++.h>
using namespace std;
typedef long long ll;
typedef double db;
#define int long long
const int N=1e5+5;
const double eps=1e-10;
const int mod=1e9+7;
#define endl '\n'

int n,m;

struct node{
    int first,second;
    inline bool operator<(const node &x)const{
        return second>x.second;
    }
};

inline int mo(int a,int b){
    return (a+b)>=n?a+b-n:a+b;
}
void solve() {
    cin>>n>>m;
    vector<int>a(n+5),vis(n+5);
    for(int i=0;i<n;i++){
        cin>>a[i];
    }
    priority_queue<node>q;
    int ans=n+1;
    q.push({0,0});
    while(!q.empty()) {
        auto y = q.top();
        q.pop();
        if (y.second >= ans)continue;
        if(vis[y.first])continue;
        vis[y.first]=1;
        int p = a[y.first];
        if (mo(y.first , p) > m) {
            ans = min(ans, n - (mo(y.first , p)) + m + 1 + y.second);
        } else {
            ans = min(ans, m - (mo(y.first , p)) + 1 + y.second);
        }
        int l = 1;
        while (mo(y.first , p)  !=m) {
            l++;
            if (y.second + l > ans) break;
            if(vis[mo(y.first , p)]==0) q.push({mo(y.first , p) , y.second + l});
            p=mo(p,1);
        }
    }
    cout<<ans<<endl;
}
signed main(){
    ios::sync_with_stdio(false);
    cin.tie(nullptr);cout.tie(nullptr);
    //cout<<fixed<<setprecision(12);
    int T=1;
    //  cin>>T;
    while(T--) solve();
    return 0;
}