#include <bits/stdc++.h>
using namespace std;
int n, a[250000];
long long ans = 0;
int main() {
  cin >> n;
  for (int i = 0; i < n; i++) {
    cin >> a[i];
    if (a[i + 1] > a[i]) ans += a[i + 1] - a[i];
  }
  for (int i = 0; i < n; i++) {
    if (a[i + 1] > a[i]) ans += a[i + 1] - a[i];
  }
  cout << ans;
  return 0;
}
