#ifdef __AVX2__
#pragma GCC target "avx2"
#endif
#pragma GCC optimize "O3"
#pragma GCC optimize "unroll-loops"
#include <bits/stdc++.h>
#include <ext/pb_ds/assoc_container.hpp>
#include <ext/pb_ds/tree_policy.hpp>
using namespace __gnu_pbds;
using namespace std;
#define int long long
#define elif else if
#define all(l) begin(l),end(l)
#define rall(l) rbegin(l),rend(l)
#define append push_back
#define print(l) for(auto i:l) cout<<i<<' '; cout<<endl;
#define pprint(a,b) cout<<a<<' '<<b<<endl;
#define inp(l) for(auto &i:l) cin>>i;
#define ordered_set tree<int, null_type,less<int>, rb_tree_tag,tree_order_statistics_node_update>
#define pai make_pair
#define endl "\n"
#define pii pair<int,int>
#define fi first
#define se second
#define vec vector
// const int mod=998244353;
const int mod1=998244353;
const int mod=1e9+7;
const int N=2e5+5;
int iter=1,itera=1;
void solve(){
int n,m;
cin>>n>>m;
vec<int>a(n);
inp(a);
int ans=0,h=0;
int ma=0;
for(auto i:a) ma=max(ma,i);
for(int i=1;i<n-1;i++){
ans+=max(1ll,a[i]-h);
h=max(h,a[i]);
if(a[i]<=h and h<ma) h++;
// cout<<a[i]-a[i-1]<<endl;
// cout<<a[i]-a[i-1]<<endl;
}
ans+=max(1ll,h);
// cout<<h<<endl;
cout<<ans<<endl;
}
signed main(){
// freopen("","r",stdin);
// freopen("","w",stdout);
ios_base::sync_with_stdio(false);
cin.tie(NULL);
cout.tie(NULL);
cout<<fixed<<setprecision(20);
// cin>>itera;
for(iter=1;iter<=itera;iter++) solve();
}
