#include<bits/stdc++.h> 
using namespace std;
using ll=long long;

ll f(ll N){
	if(__builtin_popcount(N+1)==1){
		return N-(N/2);
	}
	else{
		return N-((N+1)&(-N-1))+1;
	}
}
void solve(){
	ll N,M;
	cin>>N>>M;
	ll x=0;
	ll an=0;
	for(int i=0;i<M;i++){
		ll B;
		cin>>B;
		an+=f(B-x-1);
		x=B;
	}
	an+=f(N-x);
	cout<<an<<endl;
}

int main(){
	
	cin.tie(nullptr);
	ios::sync_with_stdio(false);

	int T=1;
	// cin>>T;
	while(T--)solve();
}