#include <iostream>
#include <vector>
#include <algorithm>

using namespace std;

int main() {
    int n, m;
    cin >> n >> m;
    vector<int> v(m);
    for (int i = 0; i < m; ++i) {
        cin >> v.at(i);
    }
    int pos = 1;
    for (int j = m -1; j >= 0; --j) {
        if (pos == 1) {
            pos = v.at(j);
        } else {
            if (pos <= v.at(j)) {
                --pos;
            }
        }
    }
    cout << pos << endl;
    return 0;
}