#include <bits/stdc++.h>
using namespace std;
int main(){
    long long n,m,s,i,x,r;
    cin>>n>>m;
    s = 0;
     
    //m次移动
    for(i = 1;i <= m;i++){
        cin>>x;
        s = s + x; 
    }
     
    //去掉完整的若干来回，实际还需要走几个格子
    s = s % ((n - 1) * 2); 
    //如果是向右能走完
    if(s <= n - 1){
        r = 1 + s;
    } else{
        r = n - s % (n - 1);
    }
    cout<<r<<endl;
     
    return 0;
}
/**************************************************************
	Problem: 1543
	User: lijinkai
	Language: C++
	Result: Accepted
	Time:104 ms
	Memory:2072 kb
****************************************************************/