#include #define all(v) v.begin(), v.end() #define rall(v) v.rbegin(), v.rend() #define rep(i,n) for(int i=0;i<(int)(n);i++) #define drep(i,j,n) for(int i=0;i<(int)(n-1);i++)for(int j=i+1;j<(int)(n);j++) #define trep(i,j,k,n) for(int i=0;i<(int)(n-2);i++)for(int j=i+1;j<(int)(n-1);j++)for(int k=j+1;k<(int)(n);k++) #define codefor int test;scanf("%d",&test);while(test--) #define INT(...) int __VA_ARGS__;in(__VA_ARGS__) #define LL(...) ll __VA_ARGS__;in(__VA_ARGS__) #define Yes(ans) if(ans)printf("Yes\n");else printf("No\n") #define YES(ans) if(ans)printf("YES\n");else printf("NO\n") #define popcount(v) __builtin_popcountll(v) #define vector1d(type,name,...) vectorname(__VA_ARGS__) #define vector2d(type,name,h,...) vector>name(h,vector(__VA_ARGS__)) #define vector3d(type,name,h,w,...) vector>>name(h,vector>(w,vector(__VA_ARGS__))) #define vector4d(type,name,h,w,d,...) vector>>>name(h,vector>>(w,vector>(d,vector(__VA_ARGS__)))) using namespace std; using ll = long long; templateusing rpriority_queue = priority_queue, greater>; const int MOD=1000000007; const int MOD2=998244353; const int INF=1<<30; const ll INF2=(ll)1<<60; //入力系 void scan(int& a){scanf("%d",&a);} void scan(long long& a){scanf("%lld",&a);} templatevoid scan(pair& p){scan(p.first);scan(p.second);} template void scan(T& a){cin>>a;} template void scan(vector& vec){for(auto&& it:vec)scan(it);} void in(){} template void in(Head& head, Tail&... tail){scan(head);in(tail...);} //出力系 void print(const int& a){printf("%d",a);} void print(const long long& a){printf("%lld",a);} void print(const double& a){printf("%.15lf",a);} templatevoid print(const pair& p){print(p.first);putchar(' ');print(p.second);} template void print(const T& a){cout< void print(const vector& vec){if(vec.empty())return;print(vec[0]);for(auto it=vec.begin();++it!= vec.end();){putchar(' ');print(*it);}} void out(){putchar('\n');} template void out(const T& t){print(t);putchar('\n');} template void out(const Head& head,const Tail&... tail){print(head);putchar(' ');out(tail...);} //デバッグ系 template void dprint(const T& a){cerr< void dprint(const vector& vec){if(vec.empty())return;cerr< void debug(const T& t){dprint(t);cerr< void debug(const Head& head, const Tail&... tail){dprint(head);cerr<<" ";debug(tail...);} ll intpow(ll a, ll b){ ll ans = 1; while(b){ if(b & 1) ans *= a; a *= a; b /= 2; } return ans; } ll modpow(ll a, ll b, ll p){ ll ans = 1; while(b){ if(b & 1) (ans *= a) %= p; (a *= a) %= p; b /= 2; } return ans; } ll modinv(ll a, ll m) {ll b = m, u = 1, v = 0;while (b) {ll t = a / b;a -= t * b; swap(a, b);u -= t * v; swap(u, v);}u %= m;if (u < 0) u += m;return u;} ll updivide(ll a,ll b){if(a%b==0) return a/b;else return (a/b)+1;} template void chmax(T &a,const T b){if(b>a)a=b;} template void chmin(T &a,const T b){if(b>= 1; } return r; } constexpr bool is_prime_constexpr(int n) { if (n <= 1) return false; if (n == 2 || n == 7 || n == 61) return true; if (n % 2 == 0) return false; long long d = n - 1; while (d % 2 == 0) d /= 2; constexpr long long bases[3] = {2, 7, 61}; for (long long a : bases) { long long t = d; long long y = pow_mod_constexpr(a, t, n); while (t != n - 1 && y != 1 && y != n - 1) {y = y * y % n;t <<= 1;} if (y != n - 1 && t % 2 == 0) {return false;} } return true; } template constexpr bool is_prime = is_prime_constexpr(n); constexpr std::pair inv_gcd(long long a, long long b) { a = safe_mod(a, b); if (a == 0) return {b, 0}; long long s = b, t = a; long long m0 = 0, m1 = 1; while (t) {long long u = s / t;s -= t * u;m0 -= m1 * u;auto tmp = s;s = t;t = tmp;tmp = m0;m0 = m1;m1 = tmp;} if (m0 < 0) m0 += b / s; return {s, m0}; } constexpr int primitive_root_constexpr(int m) { if (m == 2) return 1; if (m == 167772161) return 3; if (m == 469762049) return 3; if (m == 754974721) return 11; if (m == 998244353) return 3; int divs[20] = {}; divs[0] = 2; int cnt = 1; int x = (m - 1) / 2; while (x % 2 == 0) x /= 2; for (int i = 3; (long long)(i)*i <= x; i += 2) { if (x % i == 0) {divs[cnt++] = i;while (x % i == 0) {x /= i;}} } if (x > 1) {divs[cnt++] = x;} for (int g = 2;; g++) { bool ok = true; for (int i = 0; i < cnt; i++) { if (pow_mod_constexpr(g, (m - 1) / divs[i], m) == 1) {ok = false;break;} } if (ok) return g; } } template constexpr int primitive_root = primitive_root_constexpr(m); unsigned long long floor_sum_unsigned(unsigned long long n,unsigned long long m,unsigned long long a,unsigned long long b) { unsigned long long ans = 0; while (true) { if (a >= m) {ans += n * (n - 1) / 2 * (a / m);a %= m;} if (b >= m) {ans += n * (b / m);b %= m;} unsigned long long y_max = a * n + b; if (y_max < m) break; n = (unsigned long long)(y_max / m); b = (unsigned long long)(y_max % m); std::swap(m, a); } return ans; } template using is_integral = typename std::is_integral; template using is_signed_int = typename std::conditional::value && std::is_signed::value, std::true_type, std::false_type>::type; template using is_unsigned_int = typename std::conditional::value && std::is_unsigned::value, std::true_type, std::false_type>::type; template using to_unsigned = typename std::conditional::value, std::make_unsigned, std::common_type>::type; template using is_signed_int_t = std::enable_if_t::value>; template using is_unsigned_int_t = std::enable_if_t::value>; template using to_unsigned_t = typename to_unsigned::type; struct modint_base {}; struct static_modint_base : modint_base {}; template using is_modint = std::is_base_of; template using is_modint_t = std::enable_if_t::value>; } // namespace internal template * = nullptr> struct static_modint : internal::static_modint_base { using mint = static_modint; public: static constexpr int mod() { return m; } static mint raw(int v) {mint x;x._v = v;return x;} static_modint() : _v(0) {} template * = nullptr> static_modint(T v) { long long x = (long long)(v % (long long)(umod())); if (x < 0) x += umod();_v = (unsigned int)(x); } template * = nullptr> static_modint(T v) {_v = (unsigned int)(v % umod());} unsigned int val() const { return _v; } mint& operator++() {_v++;if (_v == umod()) _v = 0;return *this;} mint& operator--() {if (_v == 0) _v = umod();_v--;return *this;} mint operator++(int) {mint result = *this;++*this;return result;} mint operator--(int) {mint result = *this;--*this;return result;} mint& operator+=(const mint& rhs) {_v += rhs._v;if (_v >= umod()) _v -= umod();return *this;} mint& operator-=(const mint& rhs) {_v -= rhs._v;if (_v >= umod()) _v += umod();return *this;} mint& operator*=(const mint& rhs) {unsigned long long z = _v;z *= rhs._v;_v = (unsigned int)(z % umod());return *this;} mint& operator/=(const mint& rhs) { return *this = *this * rhs.inv(); } mint operator+() const { return *this; } mint operator-() const { return mint() - *this; } mint pow(long long n) const {assert(0 <= n);mint x = *this, r = 1;while (n) {if (n & 1) r *= x;x *= x;n >>= 1;}return r;} mint inv() const {if (prime) {assert(_v);return pow(umod() - 2);} else {auto eg = internal::inv_gcd(_v, m);assert(eg.first == 1);return eg.second;}} friend mint operator+(const mint& lhs, const mint& rhs) {return mint(lhs) += rhs;} friend mint operator-(const mint& lhs, const mint& rhs) {return mint(lhs) -= rhs;} friend mint operator*(const mint& lhs, const mint& rhs) {return mint(lhs) *= rhs;} friend mint operator/(const mint& lhs, const mint& rhs) {return mint(lhs) /= rhs;} friend bool operator==(const mint& lhs, const mint& rhs) {return lhs._v == rhs._v;} friend bool operator!=(const mint& lhs, const mint& rhs) {return lhs._v != rhs._v;} //自分で加えたもの friend istream& operator>>(istream& os,mint& rhs) noexcept { long long v; rhs = mint{(os >> v, v)}; return os; } friend constexpr ostream& operator << (ostream &os, const mint& rhs) noexcept { return os << rhs._v; } private: unsigned int _v; static constexpr unsigned int umod() { return m; } static constexpr bool prime = internal::is_prime; }; using mint=static_modint<1000000007>; using mint2=static_modint<998244353>; int main(){ int n; in(n); vector a(n); in(a); ll ans = 0; for(int j = 0; j < 1000; j++){ for(int i = 1; i + 1 < n; i += 2){ if(a[i - 1] < a[i] && a[i] > a[i + 1]){ ans++; a[i] = min(a[i - 1], a[i + 1]) - 1; } } for(int i = 2; i + 1 < n; i += 2){ if(a[i - 1] < a[i] && a[i] > a[i + 1]){ ans++; a[i] = min(a[i - 1], a[i + 1]) - 1; } } } /*for(int i = 0; i < n; i++){ if(i)cerr << " "; cerr << a[i]; } cerr << '\n';*/ for(int i = 1; i + 1 < n; i += 2){ ll cnt = 0; while(i + 1 < n && a[i - 1] < a[i] && a[i] > a[i + 1]){ cnt++; i += 2; } ans += cnt * (cnt + 1) / 2; } out(ans); }