求调20pts

#include<bits/stdc++.h>
using namespace std;
#define int long long
int n,m;
int k[5000005];
signed main(){
    cin>>n>>m;
    for(int i=1;i<=n;i++)cin>>k[i];
    int cnt=0,c2=1;
    for(int i=1;i<=n;i++)
    {
        cnt++;
        int l=max(c2-k[i],1ll),r=min(c2+k[i],m);
        // cout<<l<<endl<<r<<endl;
        cnt+=r-l+1;
        if(c2==1)
        {
        	if(r==m)c2=m;
            else c2=2;
		}
        else{
            if(l==1)c2=1;
            else c2=m-1;
        }
    }
    cout<<cnt<<endl;
}