#define _USE_MATH_DEFINES
#include <iostream>
#include <string>
#include <algorithm>
#include <vector>
#include <queue>
#include <math.h>
#include <cmath>
#include <stack>
#include <map>
#include <set>
#include <numeric>
#include <iomanip>
#include <climits>
#include <functional>
#include <cassert>
#include <tuple>
using namespace std;
using ll = long long;

int N;
int A[101010];

int main() {

    cin >> N;
    for(int i = 0; i < N; ++i) cin >> A[i];
    int ans = 0, pre = 0;
    for(int i = 0; i < N; ++i) {
        ans += A[i]-pre-1;
        pre = A[i];
    }

    cout << ans << endl;
    
}