#include <bits/stdc++.h>

using namespace std;
#define int long long
#define app push_back
const int maxn=2e5+5;
bitset<maxn> b;
int32_t main()
{
    ios_base::sync_with_stdio(false);cin.tie(0);cout.tie(0);
    int l,n;cin>>l>>n;
    int a[n];for(int i=0;i<n;++i) cin>>a[i];
    int s=a[0];
    b[0]=1;
    for(int j=1;j<n;++j)
    {
        int diff=a[j]-a[j-1];
        b=b | (b<<diff);
    }
    int res=l;
    for(int s1=0;s1<maxn;++s1)
    {
        if(b[s1])
        {
            res=min(res,abs(l-2*(s+s1)));
        }
    }
    cout<<res;
    return 0;
}