#include <bits/stdc++.h>
using namespace std;
#define rep(i, n) for (int i = 0; i < (n); i++)
typedef long long ll;
typedef pair<int, int> pii;
typedef vector<ll> vll;
typedef vector<int> vi;
typedef vector<vector<int>> vvi;
typedef vector<vector<ll>> vvll;
const ll inf = 1e16;
const ll md = 1000000007;

int main() {
  int n;
  cin>>n;
  vi bb(n);
  rep(i,n) cin>>bb[i];
  ll ans=0LL;
  ll ball=0LL;
  rep(i,n){
    ans+=abs(ball);
    ball+=bb[i]-1;
    //cout<<ans<<" "<<ball<<endl;
  }
  cout<<ans<<endl;
  return 0;
}