#include #define rep(i,n) for(int i = 0; i < (n); ++i) #define rep1(i,n) for(int i = 1; i <= (n); ++i) #define drep(i,n) for(int i = (n)-1; i >= 0; --i) #define srep(i,s,t) for (int i = s; i < (t); ++i) #define rng(a) a.begin(),a.end() #define rrng(a) a.rbegin(),a.rend() #define fi first #define se second #define pb push_back #define eb emplace_back #define pob pop_back #define sz(x) (int)(x).size() #define pcnt __builtin_popcountll #define snuke srand((unsigned)clock()+(unsigned)time(NULL)); #define newline puts("") using namespace std; template using vc = vector; template using vv = vc>; template using PQ = priority_queue,greater>; using uint = unsigned; using ull = unsigned long long; using vi = vc; using vvi = vv; using vvvi = vv; using ll = long long; using vl = vc; using vvl = vv; using vvvl = vv; using P = pair; using vp = vc

; using vvp = vv

; int geti(){int x;scanf("%d",&x);return x;} vi pm(int n, int s=0) { vi a(n); iota(rng(a),s); return a;} templateistream& operator>>(istream&i,pair&v){return i>>v.fi>>v.se;} templateostream& operator<<(ostream&o,const pair&v){return o<istream& operator>>(istream&i,vc&v){rep(j,sz(v))i>>v[j];return i;} templatestring join(const T&v,const string& d=""){stringstream s;rep(i,sz(v))(i?s<ostream& operator<<(ostream&o,const vc&v){if(sz(v))o<void operator--(pair&a,int){a.fi--;a.se--;} templatevoid operator++(pair&a,int){a.fi--;a.se--;} templatevoid operator--(vc&a,int){for(T&x:a)x--;} templatevoid operator++(vc&a,int){for(T&x:a)x++;} templatevoid operator+=(vc&a,T b){for(T&x:a)x+=b;} templatevoid operator+=(vc&a,const vc&b){a.insert(a.end(),rng(b));} templatebool mins(T1& x,const T2&y){if(ybool maxs(T1& x,const T2&y){if(xTx dup(Tx x, Ty y){return (x+y-1)/y;} templatell suma(const vc&a){ll res(0);for(auto&&x:a)res+=x;return res;} templatell suma(const vv&a){ll res(0);for(auto&&x:a)res+=suma(x);return res;} templatevoid uni(T& a){sort(rng(a));a.erase(unique(rng(a)),a.end());} templatevoid prepend(vc&a,const T&x){a.insert(a.begin(),x);} const double eps = 1e-10; const ll LINF = 1001002003004005006ll; const int INF = 1001001001; #define dame { puts("-1"); return;} #define yes { puts("Yes"); return;} #define no { puts("No"); return;} #define rtn(x) { cout<<(x)<=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=(ull)x*a.x%mod; return *this;} mint& operator/=(const mint& a) { x=(ull)x*a.pow(mod-2).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 operator/(const mint& a) const { return mint(*this) /= a;} mint pow(ll t) const { mint res = 1; for (mint p=x;t;p*=p,t>>=1) if (t&1) res *= p; return res; } mint ppow(ll t) const { int p=mod-1; return pow((t%p+p)%p);} bool operator<(const mint& a) const { return x < a.x;} bool operator==(const mint& a) const { return x == a.x;} bool operator!=(const mint& a) const { return x != a.x;} }; mint ex(mint x, ll t) { return x.pow(t);} istream& operator>>(istream&i,mint&a) {i>>a.x;return i;} //* ostream& operator<<(ostream&o,const mint&a) {o< y+i) a = s?-y:y, b = i; } o<; using vvm = vector; struct modinv { int n; vm d; modinv(): n(2), d({0,1}) {} mint operator()(int i) { while (n <= i) d.pb(-d[mod%n]*(mod/n)), ++n; return d[i];} mint operator[](int i) const { return d[i];} } invs; struct modfact { int n; vm d; modfact(): n(2), d({1,1}) {} mint operator()(int i) { while (n <= i) d.pb(d.back()*n), ++n; return d[i];} mint operator[](int i) const { return d[i];} } facs; struct modfactinv { int n; vm d; modfactinv(): n(2), d({1,1}) {} mint operator()(int i) { while (n <= i) d.pb(d.back()*invs(n)), ++n; return d[i];} mint operator[](int i) const { return d[i];} } ifacs; mint comb(int a, int b) { if (a < b || b < 0) return 0; return facs(a)*ifacs(b)*ifacs(a-b); } struct modpow { mint x; int n; vm d; modpow(mint x=2): x(x), n(1), d(1,1) {} mint operator()(int i) { while (n <= i) d.pb(d.back()*x), ++n; return d[i];} mint operator[](int i) const { return d[i];} } two(2);//, owt(invs(2)); // struct Solver { void solve() { int n,m; scanf("%d%d",&n,&m); vi a(n); cin>>a; { int x = 0; rep(i,n) x = (a[i]-x+m)%m; if (x) dame; } vm s(n), t(n); vi u(n); s[n-1] = 0; t[n-1] = 1; u[n-1] = 0; drep(i,n-1) { s[i] = s[i+1]*(m-2)+t[i+1]; t[i] = s[i+1]*(m-1); u[i] = (u[i+1]-1+m)%m; } mint ans = 1; rep(i,n) { mint now = s[i]*a[i]; if (u[i] < a[i]) now += t[i]-s[i]; ans += now; } cout<