#include<bits/stdc++.h>
using namespace std;
constexpr int Inf = 2000000000;
constexpr long long INF= 2000000000000000000;

template<typename T> inline bool chmax(T &a, T b) { if (a < b) { a = b; return true; } return false; }
template<typename T> inline bool chmin(T &a, T b) { if (a > b) { a = b; return true; } return false; }

template<typename T,typename U>
T modpow(T N, U P, T M = -1) {
    if(P < 0) return 0;
    T ret = 1;
    if(M != -1) ret %= M;
    while(P) {
        if(P & 1) {
            if(M == -1) ret *= N;
            else ret = ret * N % M;
        }
        P /= 2;
        if(M == -1) N *= N;
        else N = N * N % M;
    }
    return ret;
}

template <typename F>
struct FixPoint : F {
    template <typename G>
    FixPoint(G&& g) : F{std::forward<G>(g)} {}

    template <typename... Args>
    decltype(auto)
    operator()(Args&&... args) const {
        return F::operator()(*this, std::forward<Args>(args)...);
    }
};

#if defined(__cpp_deduction_guides)
template <typename F>
FixPoint(F&&)
    -> FixPoint<std::decay_t<F>>;
#endif  // defined(__cpp_deduction_guides)

template <typename F>
inline FixPoint<std::decay_t<F>>
fix(F&& f) {
    return std::forward<std::decay_t<F>>(f);
}

constexpr long long MOD = 998244353;

int main() {
    int n;
    cin >> n;
    vector<int> vec(n);
    for(auto& x: vec) cin >> x;

    vector<int> diff(n - 1);
    for(int i = 0;i < n - 1;i++) {
        diff[i] = vec[i + 1] - vec[i];
    }
    diff.push_back(0);

    long long ret = 0;
    long long now = 0;
    for(int i = 0;i < n ;i++) {
        if(diff[i] == 1) now++;
        else {
            ret += now * (now + 1) / 2;
            now = 0;
        }
    }

    cout << ret << endl;
}