#include <iostream>
#include <cstdint>
#include <vector>
#include <set>
#include <functional>

using namespace std;

int main()
{
	cin.tie(nullptr);
	ios::sync_with_stdio(false);

	uint32_t N, i;
	cin >> N;
	vector<uint32_t> A(N);
	for (i = 0; i != N; ++i) cin >> A[i];

	uint64_t ans = A[0] - 1;
	for (i = 1; i != N; ++i)
		ans += A[i] - A[i - 1] - 1;

	cout << ans << '\n';
	return 0;
}