CodeForces-339B-Xenia and Ringroad

B. Xenia and Ringroad

time limit per test

2 seconds

memory limit per test

256 megabytes

input

standard input

output

standard output

Xenia lives in a city that has n houses built along the main ringroad. The ringroad houses are numbered 1 through n in the clockwise order. The ringroad traffic is one way and also is clockwise.

Xenia has recently moved into the ringroad house number 1. As a result, she's got m things to do. In order to complete the i-th task, she needs to be in the house number ai and complete all tasks with numbers less than i. Initially, Xenia is in the house number 1, find the minimum time she needs to complete all her tasks if moving from a house to a neighboring one along the ringroad takes one unit of time.

Input

The first line contains two integers n and m (2 ≤ n ≤ 105, 1 ≤ m ≤ 105). The second line contains m integersa1, a2, ..., am (1 ≤ ai ≤ n). Note that Xenia can have multiple consecutive tasks in one house.

Output

Print a single integer — the time Xenia needs to complete all tasks.

Please, do not use the %lld specifier to read or write 64-bit integers in С++. It is preferred to use the cin, coutstreams or the %I64d specifier.

Sample test(s)

input

4 3
3 2 3

output

6

input

4 3
2 3 3

output

2

Note

In the first test example the sequence of Xenia's moves along the ringroad looks as follows: 1 → 2 → 3 → 4 → 1 → 2 → 3. This is optimal sequence. So, she needs 6 time units.

注意：第一次提交無法AC原因在於題目要求的數據範圍最高達10^5，之前採用int型無法容納導致溢出

#include<iostream>

using namespace std;

int main()
{
	long long n, m;
	cin >> n >> m;
	long long temp, total = 0,last_position=1;
	while (m--){
		cin >> temp;
		total += (temp >= last_position) ? (temp - last_position) : (n - (last_position - temp));
		last_position = temp;
	}
	cout << total << endl;
	return 0;
	
}