#define _CRT_SECURE_NO_WARNINGS
#include <stdio.h>
#include <algorithm>
#include <utility>
#include <functional>
#include <cstring>
#include <queue>
#include <stack>
#include <math.h>
#include <iterator>
#include <vector>
#include <string>
#include <set>
#include <math.h>
#include <iostream> 
#include<map>
#include <iomanip>
#include <stdlib.h>
#include <list>
#include <typeinfo>
#include <list>
#include <set>
using namespace std;
#define MAX_MOD 1000000007
#define REP(i,n) for(long long i = 0;i < n;++i)
#define LONGINF 1000000000000000000
int hoge[200000] = {};
int main() {
	int n, m;
	cin >> n >> m;
	int now = 1;
	vector<int> reversing;
	REP(i, m) {
		int tmp;
		cin >> tmp;
		reversing.push_back(tmp);
	}
	reverse(reversing.begin(), reversing.end());
	for (int i = 0;i < m;++i) {
		int tmp = reversing[i];
		if (now == 1) {
			now = tmp;
		}
		else if (now <= tmp) {
			now--;
		}
	}
	cout << now << endl;
	return 0;
}