Codeforces 339B：Xenia and Ringroad（水题）

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 $a_i$ 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 $m$ $(2 ≤ n ≤ 10^5, 1 ≤ m ≤ 10^5)$. The second line contains $m$ integers $a_1, a_2, ..., a_m (1 ≤ a_i ≤ n)$. 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, cout streams or the %I64d specifier.

Examples

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.

题意

有$n$个点围成的圆，每个点编号$1$~$n$，要求第$i$个点的任务必须在$a_i$点完成，并且必须按照顺序去完成任务。计算完成所有任务需要花费的最小时间（移动一个点花费时间为$1$）

嘤嘤嘤，题意读了一年，真的是废了

Code

/*************************************************************************

	 > Author: WZY
	 > School: HPU
	 > Created Time:   2019-03-26 15:36:37
	 
************************************************************************/
#include <cmath>
#include <cstdio>
#include <time.h>
#include <cstring>
#include <limits.h>
#include <iostream>
#include <algorithm>
#include <random>
#include <iomanip>
#include <map>
#include <set>
#include <stack>
#include <queue>
#include <vector>
#include <string>
#include <random>
#define ll long long
#define ull unsigned long long
#define lson o<<1
#define rson o<<1|1
#define ms(a,b) memset(a,b,sizeof(a))
#define SE(N) setprecision(N)
#define PSE(N) fixed<<setprecision(N)
#define bug cout<<"-------------"<<endl
#define debug(...) cerr<<"["<<#__VA_ARGS__":"<<(__VA_ARGS__)<<"]"<<"
"
#define LEN(A) strlen(A)
const double E=exp(1);
const double eps=1e-9;
const double pi=acos(-1.0);
const int mod=1e9+7;
const int maxn=1e6+10;
const int maxm=1e3+10;
const int moha=19260817;
const int inf=1<<30;
const ll INF=1LL<<60;
using namespace std;
inline void Debug(){cerr<<'
';}
inline void MIN(int &x,int y) {if(y<x) x=y;}
inline void MAX(int &x,int y) {if(y>x) x=y;}
inline void MIN(ll &x,ll y) {if(y<x) x=y;}
inline void MAX(ll &x,ll y) {if(y>x) x=y;}
template<class FIRST, class... REST>void Debug(FIRST arg, REST... rest){
	cerr<<arg<<"";Debug(rest...);}
int a[maxn];
int vis[maxn];
int main(int argc, char const *argv[])
{
	ios::sync_with_stdio(false);cin.tie(0);
	cout.precision(20);
	#ifndef ONLINE_JUDGE
	    freopen("in.txt", "r", stdin);
	    freopen("out.txt", "w", stdout);
		srand((unsigned int)time(NULL));
	#endif
	int n,m;
	cin>>n>>m;
	for(int i=1;i<=m;i++)
		cin>>a[i];
	ll ans=0;
	int res=1;
	vis[res]=1;
	ans+=a[1]-1;
	while(res<m)
	{
		if(a[res]>a[res+1])
			ans+=(n-a[res])+a[res+1];
		else if(a[res]==a[res+1])
		{
			res++;
			continue;
		}
		else
			ans+=(a[res+1]-a[res]);
		res++;
	}
	cout<<ans<<endl;
	#ifndef ONLINE_JUDGE
	    cerr<<"Time elapsed: "<<1.0*clock()/CLOCKS_PER_SEC<<" s.
";
	#endif
	return 0;
}