#if !defined(__clang__) && defined(__GNUC__)
#include <bits/stdc++.h>
#else
#include <cstdlib>
#include <climits>
#include <iostream>
#include <cstdint>
#include <vector>
#include <string>
#include <complex>
#include <bitset>
#include <queue>
#include <deque>
#include <stack>
#include <utility>
#include <set>
#include <map>
#include <unordered_set>
#include <unordered_map>
#include <regex>
#endif //  !defined(__clang__) && defined(__GNUG__)

using namespace std;

int main()
{
    int64_t N, M;
    std::cin >> N >> M;

    std::vector<int64_t> A;
    for (decltype(M) i = 0; i < M; ++i) {
        int64_t t;
        std::cin >> t;
        A.push_back(t);
    }

    std::reverse(std::begin(A), std::end(A));

    int64_t pos = 1;

    for (auto a: A) {
        if (pos == 1) {
            pos = a;
        }
        else if (pos > a) {
            // nop
        }
        else {
            pos = pos - 1;
        }
    }

    std::cout << pos << std::endl;

#if 0
    std::list<int64_t> A;
    for (int64_t i = 1; i <= 50; ++i) {
        A.push_back(i);
    }

    for (decltype(M) i = 1; i <= M; ++i) {
        int64_t t;
        std::cin >> t;

        A.splice(A.begin(), A, std::next(A.begin(), t-1));
    }

    std::cout << *A.begin() << std::endl;
    #endif
    return 0;
}