include <bits/stdc++.h>

typedef long long ll;
using namespace std;

int main ()
{
int n,N,a[210],i,sum=0;
cin>>n>>N;
a[0]=0;
for(i=1;i<=n;i++){
cin>>a[i];
}
for(i=1;i<n;i++){
if(N>=a[i]) sum+=(a[i+1]-a[i])i;
}
if(N>a[n]) sum+=(N-a[n])n;
cout<<sum;

return 0;

}