#include <bits/stdc++.h>
using namespace std;
#include <atcoder/all>
using namespace atcoder;
#define rep(i, n) for(int i=0;i<(n);++i)
#define rep1(i, n) for(int i=1;i<=(n);i++)
#define ll long long
using mint = modint998244353;
using P = pair<ll,ll>;
using lb = long double;
using T = tuple<ll, ll, ll>;
#ifdef LOCAL
#  include <debug_print.hpp>
#  define dbg(...) debug_print::multi_print(#__VA_ARGS__, __VA_ARGS__)
#else
#  define dbg(...) (static_cast<void>(0))
#endif

int main()
{
    int l, n;
    cin >> l >> n;
    vector<int> x(n+2);
    rep(i,n) cin >> x[i+1];
    x[n+1] = l;
    vector<vector<bitset<200005>>> dp(n+2, vector<bitset<200005>>(2));
    dp[0][0][l] = 1;
    rep(i,n+1){
        for(int j=i+1;j<=n+1;j++){
            dp[j][1] |= dp[i][0]<<(x[j]-x[i]);
            dp[j][0] |= dp[i][1]>>(x[j]-x[i]);
        }
    }
    int ans = 1e9;
    for(int j=0;j<=2*l;j++){
        if(dp[n+1][0][j]) ans = min(ans, abs(l-j));
    }
    cout << ans << endl;
    return 0;
}