#include<bits/stdc++.h>
using namespace std;
main(){
    int N,M,D[1000];
    scanf("%d%d",&N,&M);
    for(int i = 0;i < M;i++){
        scanf("%d",&D[i]);
    }
    int mini = 100000000;
    int head = M-1,tail;
    for(int i = 0;i < M;i++){
        if(D[i]>=0){
            head = i;
            break;
        }
    }

    if(head+N>M){
        tail = M-1;
        head = M-N;
    }else{
        tail = head+N-1;
    }
    while(head>=0){
        int h = abs(D[head]),t = abs(D[tail]);
        if(D[head]*D[tail] >= 0){
            mini = min(mini,max(h,t));
        }else{
            mini = min(mini,min(h,t)*2+
            max(h,t));
        }
        if(D[tail]<0)break;
        head--;tail--;
    }
    printf("%d\n",mini);
}