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