#include <bits/stdc++.h>
#define INIT std::ios::sync_with_stdio(false);std::cin.tie(0);
#define VAR(type, a) type a;std::cin>>a;
// VAR(int, x);
#define OUT(d) std::cout<<(d);
#define SP std::cout<<" ";
#define ENDL std::cout<<"\n";
#define VEC(type, c, n) std::vector<type> c(n);for(auto& i:c)std::cin>>i;
#define MAT(type, c, m, n) std::vector<std::vector<type>> c(m, std::vector<type>(n));for(auto& r:c)for(auto& i:r)std::cin>>i;
#define ALL(a) (a).begin(),(a).end()
#define FOR(i,a,b) for (int i=(a);i<(b);i++)
#define RFOR(i,a,b) for (int i=(b)-1;i>=(a);i--)
#define REP(i,n) for (int i=0;i<(n);i++)
#define RREP(i,n) for (int i=(n)-1;i>=0;i--)

using ll = long long;

int main(){
    INIT;
    VAR(int, n);VAR(int, m);
    VEC(int, d, m);
    std::sort(ALL(d));
    int l = 0, r = n-1;
    int ans = 100000;
    int zero = -1;
    REP(i, m){
        if(d[i]==0){
            zero=i;
            break;
        }
    }
    for(; r<m; ++l,++r){
        int tmp;
        if(d[r]<=0) tmp = 0-d[l];
        else if(d[l]>=0) tmp = d[r]-0;
        else tmp = d[r]-d[l]+((zero!=-1)?2:1)+std::min(std::fabs(d[l]), std::fabs(d[r]))-1;
        ans = std::min(ans, tmp);
    }
    OUT(ans)ENDL;
    return 0;
}