#include <bits/stdc++.h>

using namespace std;

#define REP(i, n) for(int i = 0; i < n; i++)
#define ALL(a) (a).begin(),(a).end()

int main() {
    int n, m;
    cin >> n >> m;

    vector<int> card(n);
    REP(i, n) card[i] = i;

    REP(i, m) {
        int t;
        cin >> t;
        card.insert(card.begin(), card[t + 1]);
        card.erase(card.begin() + (t + 1) + 1);
    }
    cout << card[0] << endl;
    return 0;
}