#include <bits/stdc++.h>
using namespace std;
#define rep(i, n) for (int i = 0; i < (int)(n); ++i)
int main() {
    // Input
    int N, M;
    cin >> N >> M;
    vector<int> A(M);
    rep(i, M) cin >> A[i];

    // Simulation
    vector<int> deck(N + 1);
    iota(deck.begin(), deck.end(), 0);
    rep(i, M) {
        int pick = deck[A[i]];
        for (int j = A[i]; j != 1; --j) deck[j] = deck[j - 1];
        deck[1] = pick;
    }

    // Output
    cout << deck[1] << endl;
}