#include "bits/stdc++.h"
using namespace std;
#define ll long long
#define endl '\n'
#define rep(i, n) for(int i = 0; i < (int)(n); i++)
#define rep2(i,a,b) for(int i=int(a);i<int(b);i++)
#define pb emplace_back
#define all(x) (x).begin(),(x).end()
int mod=1e9+7;
int mod2=998244353;
const int INF=1e9;

signed main(){
	ll n,m,t;
	cin>>n>>m>>t;
	vector<ll> c(t,1);
	ll a;
	rep(j,n){
		cin>>a;
		rep(i,m+1){
			if(a-i>=0)c[a-i]=0;
			if(a+i-1<t)c[a+i-1]=0;
		}
	}
	ll ans=0;
	rep(i,t)ans+=c[i];
	cout<<ans<<endl;
}

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