#include <bits/stdc++.h>
using namespace std;
//#pragma GCC optimize("Ofast")
#define rep(i,n) for(long long i=0;i<(long long)(n);i++)
#define REP(i,k,n) for(long long i=k;i<(long long)(n);i++)
#define RREP(i,k,n) for(long long i=n;i>=(long long)(k);i--)
#define all(a) a.begin(),a.end()
#define rall(a) a.rbegin(),a.rend()
#define pb push_back
#define eb emplace_back
#define lb(v,k) (lower_bound(all(v),k)-v.begin())
#define ub(v,k) (upper_bound(all(v),k)-v.begin())
#define fi first
#define se second
#define pi M_PI
#define PQ(T) priority_queue<T>
#define SPQ(T) priority_queue<T,vector<T>,greater<T>>
#define show(x) cout<<#x<<": "
#define newline cout<<'\n';
using ll=long long;
using S=multiset<ll>;
using P=pair<ll,ll>;
using PP=tuple<ll,ll,ll>;
using vp=vector<P>;
using vi=vector<ll>;
using vvi=vector<vi>;
using vvvi=vector<vvi>;
constexpr ll inf=1001001001001001;
constexpr int INF=1001001001;
constexpr int mod=1000000007; //or 998244353
template<class T> bool chmin(T&a,T b){if(a>b){a=b;return true;}return false;}
template<class T> bool chmax(T&a,T b){if(a<b){a=b;return true;}return false;}
template<class T> bool isin(T x,T l,T r){return (l)<=(x)&&(x)<=(r);}
template<class T> void out(T a){cout<<a<<'\n';}
template<class T> void outp(T a){cout<<'('<<a.fi<<','<<a.se<<')'<<'\n';}
template<class T> void outvp(T v){rep(i,v.size())cout<<'('<<v[i].fi<<','<<v[i].se<<')';cout<<'\n';}
template<class T> void outv(T v){rep(i,v.size()){if(i)cout<<' ';cout<<v[i];}cout<<'\n';}
template<class T> void outvv(T v){rep(i,v.size())outv(v[i]);}
template<class T> void YesNo(T b){if(b)out("Yes");else out("No");}
template<class T> void yesno(T b){if(b)out("yes");else out("no");}
template<class T> void YESNO(T b){if(b)out("YES");else out("NO");}
void decimal(int x){cout<<fixed<<setprecision(x);}
ll modpow(ll a,ll b){ll c=1;while(b>0){if(b&1){c=a*c%mod;}a=a*a%mod;b>>=1;}return c;}
vi calc(ll x){vi res;while(x>0){res.eb(x%10);x/=10;}reverse(all(res));return res;}

void solve(){
  int n,k;
  cin>>n>>k;
  vi a(n);
  rep(i,n) cin>>a[i];
  reverse(all(a));
  int sum=0;
  rep(i,n) sum+=a[i];
  int p=1,x=0;;
  rep(i,n){
    x+=p*a[i];
    p*=k;
    x%=sum; p%=sum;
  }
  out(x);
}

signed main(){
  cin.tie(0);
  ios::sync_with_stdio(false);
  solve();
}