#include <bits/stdc++.h>
#define int long long
using namespace std;
const long long N = 2e5 + 5;
int a[N];
void solve()
{
int n, m;
cin >> n >> m;
multiset<int> s;
for (int i = 0; i < n; i++)
{
cin >> a[i + 1];
s.insert(a[i + 1]);
}
int altitude = 0;
int time = n - 1;
for (int i = 2; i <= n; i++)
{
int mx = *s.rbegin();
if (altitude < mx)
{
altitude++;
}
else if (altitude > mx)
{
altitude--;
}
if (altitude < a[i])
{
time += a[i] - altitude;
altitude = a[i];
}
s.extract(a[i]);
}
cout << time + altitude << endl;
}
signed main()
{
ios_base::sync_with_stdio(0);
cin.tie(NULL);
cout.tie(NULL);
int t = 1;
// cin >> t;
for (int i = 1; i <= t; i++)
{
// cout << "Case #" << i << ':' << ' ';
solve();
cout << endl;
}
return 0;
}
