#include <bits/stdc++.h>
typedef long long ll;
using namespace std;

const int INF = 1e9;
const int MOD = 1e9+7;
const ll LINF = 1e18;

#define FOR(i,a,b) for(int i=(a);i<(b);++i)
#define REP(i,n) for(int i=0;i<(n);++i)
#define REPR(i,n) for(int i=n;i>=0;i--)
#define ALL(v) (v.begin(),v.end())
#define COUT(x) cout<<(x)<<'\n'


int main(){
    int n;
    cin >> n;
    int a[n];
    REP(i,n){
        cin >> a[i];
    }
    int max1 = a[0];
    int count = a[0]-1;
    REP(i,n){
        if(max1<a[i]){
            count += a[i]-max1-1;
            max1 = a[i];
        }
    }
    COUT(count);
    return 0;
}