#include <bits/stdc++.h>
using namespace std;
int minn=2000005, maxn;
int x;
int n, k;
int main() {
    cin>>n>>k;
    for(int i=1;i<=k;i++){
        cin>>x;
        minn=min(x, minn);
        maxn=max(x, maxn);
    }
    cout<<max(n-maxn, minn)<<endl;
    return 0;
}

这个做法为啥错了