#include <bits/stdc++.h>
using namespace std;
using ll = long long;
int main() {
  ios::sync_with_stdio(0);
  cin.tie(0);
  cout.tie(0);
  int n, m;
  cin >> n >> m;
  int arr[m];
  for (int i = 0; i < m; i++) cin >> arr[i];
  long long res = arr[0];
  for (int i = 1; i < m; i++) {
    if (arr[i] - arr[i - 1] < 0) {
      res += (n - arr[i - 1]) + arr[i];
    } else
      res += (arr[i] - arr[i - 1]);
  }
  cout << res - 1 << "\n";
  return 0;
}
