#ifdef LOCAL
#pragma GCC optimize ("O0")
#else
#pragma GCC optimize ("O3")
#endif


#include <bits/stdc++.h>

using namespace std;
using namespace std::placeholders;

using ll = long long;
using VI = vector<int>;
using VVI = vector<vector<int>>;
using VVVI = vector<vector<vector<int>>>;
using VLL = vector<ll>;
using VVLL = vector<vector<ll>>;
using VVVLL = vector<vector<vector<ll>>>;
using VB = vector<bool>;
using VVB = vector<vector<bool>>;
using PII = pair<int, int>;
using PLLI = pair<ll, int>;
const int INF = 1e9 + 7;
const int MOD = INF;
const ll INF_LL = 1e18 + 7;

#define __overload3(_1, _2, _3, name,...) name
#define rep(...) __overload3(__VA_ARGS__, repFromUntil, repUntil, repeat)(__VA_ARGS__)
#define repeat(times) repFromUntil(__name, 0, times)
#define repUntil(name, times) repFromUntil(name, 0, times)
#define repFromUntil(name, from, until) for (int name = from, name##__until = (until); name < name##__until; name++)
#define repFromTo(name, from, to) repFromUntil(name, from, to + 1)
#define repr(...) __overload3(__VA_ARGS__, reprFromUntil, reprUntil, repeat)(__VA_ARGS__)
#define reprUntil(name, times) reprFromUntil(name, 0, times)
#define reprFromUntil(name, from, until) for (int name = until - 1, name##__from = (from); name >= name##__from; name--)
#define reprFromTo(name, from, to) reprFromUntil(name, from, to + 1)

#define EXIT(out) do { OUT(out); exit(0); } while (false)

#define all(x) begin(x), end(x)
#define rall(x) rbegin(x), rend(x)

#define debugos cerr
#ifdef LOCAL
#define debug(v) do {debugos << "L" << __LINE__ << " " << #v << " > ";debugos<<(v)<<newl;} while (0)
#define debugv(v) do {debugos << "L" << __LINE__ << " " << #v << " > ";for(auto e:(v)){debugos<<e<<" ";}debugos<<newl;} while (0)
#define debuga(m,w) do {debugos << "L" << __LINE__ << " " << #m << " > ";for(int x=0;x<(w);x++){debugos<<(m)[x]<<" ";}debugos<<newl;} while (0)
#define debugaa(m,h,w) do {debugos << "L" << __LINE__ << " " << #m << " > \n";for(int y=0;y<(h);y++){for(int x=0;x<(w);x++){debugos<<(m)[y][x]<<" ";}debugos<<newl;}} while (0)
#else
#define debug(v) do {v;} while (0)
#define debugv(v) do {v;} while (0)
#define debuga(m,w) {}
#define debugaa(m,h,w) {}
#endif


#define newl "\n"

template <typename T> bool chmin(T& var, T x) {
  if (var > x) {
    var = x;
    return true;
  } else return false;
}
template <typename T> bool chmax(T& var, T x) {
  if (var < x) {
    var = x;
    return true;
  } else return false;
}

template <typename T> T divceil(T m, T d) {
  return (m+d-1)/d;
}

template <typename T> int sgn(T val) {
  return (T(0) < val) - (val < T(0));
}

PII operator+(const PII& lhs, const PII& rhs) {
  return {lhs.first + rhs.first, lhs.second + rhs.second};
}

bool p_inside(const PII& p, int h, int w) {
  return 0 <= p.first and p.first < h and 0 <= p.second and p.second < w;
}

template<typename T>
vector<T> make_v(size_t a, T b){return vector<T>(a, b);}

template<typename... Ts>
auto make_v(size_t a, Ts... ts){
  return vector<decltype(make_v(ts...))>(a, make_v(ts...));
}


class MyScanner {
public:
  template <typename T> void input_integer(T& var) {
    var = 0; T sign = 1;
    int cc = getchar();
    for (; cc<'0' || '9'<cc; cc = getchar())
      if (cc == '-') sign = -1;
    for (; '0' <= cc && cc <= '9'; cc = getchar())
      var = (var << 3) + (var << 1) + cc - '0';
    var = var * sign;
  }
  int c() { char c; while (c = getchar(), c == ' ' or c == '\n'); return c; }
  MyScanner& operator>>(char& var) { var = c(); return *this; }
  MyScanner& operator>>(int& var) { input_integer<int>(var); return *this; }
  MyScanner& operator>>(ll& var) { input_integer<ll>(var); return *this; }
  MyScanner& operator>>(string& var) {
    int cc = getchar();
    for (; !isvisiblechar(cc); cc = getchar());
    for (; isvisiblechar(cc); cc = getchar())
      var.push_back(cc);
    return *this;
  }
  template <typename T, typename U>
  MyScanner& operator>>(pair<T, U>& var) {
    return *this >> var.first >> var.second;
  }
  template <typename... Ts>
  MyScanner& operator>>(tuple<Ts...>& var) {
    return tuple_impl<tuple<Ts...>, 0, sizeof...(Ts)>(var);
  }
  template <typename Tuple, size_t I, size_t N,
            enable_if_t<I == N>* = nullptr>
  MyScanner& tuple_impl(Tuple& var) {
    return *this;
  }
  template <typename Tuple, size_t I, size_t N,
            enable_if_t<I != N>* = nullptr>
  MyScanner& tuple_impl(Tuple& var) {
    *this >> get<I>(var);
    return tuple_impl<Tuple, I+1, N>(var);
  }
  template <typename T>
  operator T() {
    T x;
    *this >> x;
    return x;
  }
  template <typename T>
  void operator()(T &t) {
    *this >> t;
  }
  template <typename T, typename... Ts>
  void operator()(T &t, Ts &...ts) {
    *this >> t;
    this->operator()(ts...);
  }
  template <typename Iter>
  void iter(Iter first, Iter last) {
    while (first != last) *this >> *first, first++;
  }
  operator double() {
    double res; scanf("%lf", &res); return res;
  }
  VI vi(int n) {
    VI res(n);
    iter(all(res));
    return res;
  }
  VLL vll(int n) {
    VLL res(n);
    iter(all(res));
    return res;
  }
private:
  int isvisiblechar(int c) {
    return 0x21 <= c && c <= 0x7E;
  }
};

class MyPrinter {
public:
  template <typename T>
  void output_integer(T var) {
    if (var == 0) { putchar('0'); return; }
    if (var < 0)
      putchar('-'),
      var = -var;
    char stack[32]; int stack_p = 0;
    while (var)
      stack[stack_p++] = '0' + (var % 10),
      var /= 10;
    while (stack_p)
      putchar(stack[--stack_p]);
  }
  MyPrinter& operator<<(char c) { putchar(c); return *this; }
  template <typename T> MyPrinter& operator<<(T var) { output_integer<T>(var); return *this; }
  MyPrinter& operator<<(char* str_p) { while (*str_p) putchar(*(str_p++)); return *this; }
  MyPrinter& operator<<(const char* str_p) { while (*str_p) putchar(*(str_p++)); return *this; }
  MyPrinter& operator<<(const string& str) {
    const char* p = str.c_str();
    const char* l = p + str.size();
    while (p < l) putchar(*p++);
    return *this;
  }
  // MyPrinter& operator<<(const modint& var) { output_integer<ll>(var.value); return *this; }
  template <typename T>
  void operator()(T x) {
    *this << x << newl;
  }
  template <typename T, typename... Ts>
  void operator()(T x, Ts ...xs) {
    *this << x << " ";
    this->operator()(xs...);
  }
  template <typename T, typename U>
  MyPrinter& operator<<(pair<T, U>& var) {
    return *this << var.first << " " << var.second;
  }
  template <typename... Ts>
  MyPrinter& operator<<(tuple<Ts...>& var) {
    return tuple_impl<tuple<Ts...>, 0, sizeof...(Ts)>(var);
  }
  template <typename Tuple, size_t I, size_t N,
            enable_if_t<I == N>* = nullptr>
  MyPrinter& tuple_impl(Tuple& var) {
    return *this;
  }
  template <typename Tuple, size_t I, size_t N,
            enable_if_t<I != N>* = nullptr>
  MyPrinter& tuple_impl(Tuple& var) {
    *this << get<I>(var) << " ";
    return tuple_impl<Tuple, I+1, N>(var);
  }
  template <typename Iter>
  void iter(Iter s, Iter t) {
    if (s == t) *this << "\n";
    else {
      for (; s != t; s++) {
        *this << *s << " \n"[next(s, 1) == t];
      }
    }
  }
  template <typename Range>
  void range(const Range& r) {
    iter(begin(r), end(r));
  }
};
MyScanner IN;
MyPrinter OUT;


int main() {
  ll n = IN;
  auto v = IN.vll(n);
  OUT(accumulate(all(v), 0LL) - (n+1)*n/2);
}


Measured memory_bytes: 3576