#include <bits/stdc++.h>
using namespace std;
long long gcd(long long a, long long b) { return b ? gcd(b, a % b) : a; }
const int MAX = 1e5;
const long long MOD = 1e9 + 7;
const long long inf = 1e18;
int a[MAX + 5];
int main() {
  ios_base::sync_with_stdio(false);
  int n, m, r, i, j;
  long long ans = 0;
  cin >> n >> m;
  a[0] = 1;
  for ((i) = (1); (i) <= (m); ++i) cin >> a[i];
  i = 0;
  while (i < m) {
    if (a[i + 1] > a[i])
      ans += (a[i + 1] - a[i]);
    else if (a[i + 1] < a[i])
      ans += (n - a[i] + a[i + 1]);
    i++;
  }
  cout << ans;
}
