#include <iostream> #include <vector> #include <cmath> #include <map> #include <set> #include <iomanip> #include <queue> #include <algorithm> #include <numeric> #include <deque> #include <complex> #include <cassert> using namespace std; using ll = long long; int main(){ ll N, cnt=0, A, B=0; cin >> N; for (int i=0; i<N; i++){ cin >> A; cnt += A-B-1; B = A; } cout << cnt << endl; return 0; }