#pragma GCC optimize("Ofast") #include using namespace std; using ll = long long int ; using ld = long double ; using P = pair; using Graph= vector>; struct edge{ll to ; ll cost ;} ; using graph =vector> ; #define rep(i,n) for (ll i=0; i < (n); ++i) #define rep2(i,n,m) for(ll i=n;i<=m;i++) #define rep3(i,n,m) for(ll i=n;i>=m;i--) #define pb push_back #define eb emplace_back #define ppb pop_back #define mpa make_pair #define fi first #define se second #define set20 cout<= mod) x -= mod; return *this; } mint& operator-=(const mint a) { if ((x += mod-a.x) >= mod) x -= mod; return *this; } mint& operator*=(const mint a) { (x *= a.x) %= mod; return *this;} mint operator+(const mint a) const { return mint(*this) += a;} mint operator-(const mint a) const { return mint(*this) -= a;} mint operator*(const mint a) const { return mint(*this) *= a;} mint pow(ll t) const { if (!t) return 1; mint a = pow(t>>1); a *= a; if (t&1) a *= *this; return a; } // for prime mod mint inv() const { return pow(mod-2);} mint& operator/=(const mint a) { return *this *= a.inv();} mint operator/(const mint a) const { return mint(*this) /= a;} }; istream& operator>>(istream& is, const mint& a) { return is >> a.x;} ostream& operator<<(ostream& os, const mint& a) { return os << a.x;} //昆布 struct combination { vector fact, ifact; combination(int n):fact(n+1),ifact(n+1) { assert(n < mod); //任意modではここ消すcombmain内に fact[0] = 1; for (int i = 1; i <= n; ++i) fact[i] = fact[i-1]*i; ifact[n] = fact[n].inv(); for (int i = n; i >= 1; --i) ifact[i-1] = ifact[i]*i; } mint operator()(int n, int k) { if (k < 0 || k > n) return 0; return fact[n]*ifact[k]*ifact[n-k]; } mint p(int n,int k){ return fact[n]*ifact[n-k] ; //kは個数 } } co(1000005) ; mint modpow(ll a,ll b){ if(b==0) return 1 ; mint c= modpow(a,b/2) ; if(b%2==1) return c*c*a ; else return c*c ; } mint mmodpow(mint a,ll b){ if(b==0) return 1ll ; mint c=mmodpow(a,(b/2)) ; if(b%2==1) return c*c*a ; else return c*c ; } mint komb(ll n,ll m){ mint x=1 ;mint y=1 ; rep(i,m){ x*= n-i ; y*= i+1 ; } return x/y ; } map factor(ll n){ //素因数とオーダーをマップで管理 map ord ; for(ll i=2;i*i<=n;i++){ if(n%i==0){ int res=0; while(n%i==0){ n/=i; res++; } ord[i]=res; } } if(n!=1) ord[n]++; return ord ; } struct UnionFind { vector d; UnionFind(int n=0): d(n,-1) {} int find(int x) { if (d[x] < 0) return x; return d[x] = find(d[x]); } bool unite(int x, int y) { x = find(x); y = find(y); if (x == y) return false; if (d[x] > d[y]) swap(x,y); d[x] += d[y]; d[y] = x; return true; } bool same(int x, int y) { return find(x) == find(y);} int size(int x) { return -d[find(x)];} }; // sum(x) x以下の和 // sum(a,b) a以上b以下の和 template struct BIT { int n; vector d; BIT(int n=0):n(n),d(n+1) {} void add(int i, T x=1) { //x=1ならsumは個数のカウント for (i++; i <= n; i += i&-i) { d[i] += x; } } T sum(int i) { T x = 0; for (i++; i; i -= i&-i) { x += d[i]; } return x; } T sum(int i,int j) { if(i>0) return sum(j)-sum(i-1); else return sum(j); } }; template< typename flow_t > struct Dinic { const flow_t INF; struct edge { int to; flow_t cap; int rev; bool isrev; int idx; }; vector< vector< edge > > graph; vector< int > min_cost, iter; Dinic(int V) : INF(numeric_limits< flow_t >::max()), graph(V) {} void add_edge(int from, int to, flow_t cap, int idx = -1) { graph[from].emplace_back((edge) {to, cap, (int) graph[to].size(), false, idx}); graph[to].emplace_back((edge) {from, 0, (int) graph[from].size() - 1, true, idx}); } bool bfs(int s, int t) { min_cost.assign(graph.size(), -1); queue< int > que; min_cost[s] = 0; que.push(s); while(!que.empty() && min_cost[t] == -1) { int p = que.front(); que.pop(); for(auto &e : graph[p]) { if(e.cap > 0 && min_cost[e.to] == -1) { min_cost[e.to] = min_cost[p] + 1; que.push(e.to); } } } return min_cost[t] != -1; } flow_t dfs(int idx, const int t, flow_t flow) { if(idx == t) return flow; for(int &i = iter[idx]; i < graph[idx].size(); i++) { edge &e = graph[idx][i]; if(e.cap > 0 && min_cost[idx] < min_cost[e.to]) { flow_t d = dfs(e.to, t, min(flow, e.cap)); if(d > 0) { e.cap -= d; graph[e.to][e.rev].cap += d; return d; } } } return 0; } flow_t max_flow(int s, int t) { flow_t flow = 0; while(bfs(s, t)) { iter.assign(graph.size(), 0); flow_t f = 0; while((f = dfs(s, t, INF)) > 0) flow += f; } return flow; } void output() { for(int i = 0; i < graph.size(); i++) { for(auto &e : graph[i]) { if(e.isrev) continue; auto &rev_e = graph[e.to][e.rev]; cout << i << "->" << e.to << " (flow: " << rev_e.cap << "/" << e.cap + rev_e.cap << ")" << endl; } } } }; vector alldiv(ll n){ vector ans; if(n<0) n*=-1; for(ll i=1;i*i<=n;++i){ if(n%i==0){ if(i*i==n) ans.pb(i); else{ans.pb(i);ans.pb(n/i);} } } return ans; } int main(){ ios::sync_with_stdio(false) ; cin.tie(nullptr) ; ll n,m; cin>>n>>m; vector A(n); rep(i,n) cin>>A[i]; ll sum=0ll; rep(i,n){ if(i%2==0) sum+=A[i]; else sum-=A[i]; } if(sum%m){ cout<<-1<