#include <algorithm>
#include <array>
#include <cmath>
#include <cstdio>
#include <iostream>
#include <numeric>
#include <optional>
#include <vector>

using namespace std;

int main() {
    int32_t n, m;
    cin >> n >> m;
    vector<int32_t> as(m);
    for (auto i = 0; i < m; ++i) {
        cin >> as[i];
    }
    int32_t pos = 1;
    for (auto i = m - 1; i >= 0; --i) {
        if (pos == 1)
            pos = as[i];
        else if (pos <= as[i])
            --pos;
    }
    cout << pos << endl;
    return 0;
}