#include #include #include #include #include #include #include #include #include #include #include #include #include #include #include using namespace std; using ll = long long; using vi = vector; using vvi = vector; using vl = vector; using vvl = vector; using vb = vector; using vvb = vector; using vd = vector; using vs = vector; using pii = pair; using pll = pair; using pdd = pair; using vpii = vector; using vpll = vector; using vpdd = vector; const int inf = (1 << 30) - 1; const ll INF = 1LL << 60; //const int MOD = 1000000007; const int MOD = 998244353; int main() { int n; cin >> n; vi a(n); for (int i = 0; i < n; i++) { cin >> a[i]; } cout << a[n - 1] - n; return 0; }