#include<cstdio>
#include<cmath>
using namespace std;
int main(){
    FILE *in=fopen("transport.in","r"),*out=fopen("transport.out","w");
    bool ok=0;
    int s,k,n,t,v[16005]={0},te;
    fscanf(in,"%d%d",&n,&t);
    for(int i=0;i<n;i++){
        fscanf(in,"%d",&v[i]);
    }
    for(int i=1;i<n;i++){
        k=0;
        ok=0;
        te=0;
        for(int j=0;j<n;j++){
            if(v[j]<i){
                break;
            }
            s=0;
            if(te>0){
                te--;
                continue;
            }
            do{
                s+=v[i];
                te++;
            }
            while(s>n);
            k++;
            ok++;
        }
        if(ok==1 && k<t){
            fprintf(out,"%d",4*k);
            break;
        }
    }
    return 0;
}