// #pragma comment(linker, "/stack:200000000")
// #pragma GCC optimize("Ofast")
// #pragma GCC optimize("O3,unroll-loops")
// #pragma GCC target("sse,sse2,sse3,ssse3,sse4")
// #pragma GCC target("avx2,bmi,bmi2,popcnt,lzcnt")
 
// #define _GLIBCXX_DEBUG
// #define _GLIBCXX_DEBUG_PEDANTIC
 
#include <iomanip>
#include <cassert>
#include <iostream>
#include <vector>
#include <random>
#include <algorithm>
#include <map>
#include <set>
#include <functional>
#include <array>
#include <numeric>
#include <queue>
#include <deque>
#include <bitset>
#include <cmath>
#include <climits>
#include <cstdint>
// #include <ext/pb_ds/assoc_container.hpp> 
// #include <ext/pb_ds/tree_policy.hpp>
// #include <ext/rope>
 
// using namespace __gnu_pbds;
// using namespace __gnu_cxx;
using namespace std;
 
const int MOD = 998244353;
const long double PI = 3.141592653589793;
using ll = long long;
const ll INF = 1e18;
 
// #define int ll
// --------> sashko123`s defines:
#define itn int     //Vasya sorry :(
#define p_b push_back
#define fi first
#define se second
#define pii std::pair<int, int>
#define oo LLONG_MAX
#define big INT_MAX
#define elif else if
int input()
{
    int x;
    cin >> x;
    return x;
}
// ----------> end of sashko123`s defines (thank you Vasya <3)
// template<typename K, typename V>
// using hash_table = cc_hash_table<K, V, hash<K>>;
// template<typename T>
// using ordered_set = tree<T,null_type,less<T>,rb_tree_tag,tree_order_statistics_node_update>;
void solve() {
    int n, m, k;
    cin >> n >> m >> k;
    vector<int> used(n + 1);
    for (int i = 0; i < m; i++) {
        int p;
        cin >> p;
        for (int j = max(1, p - k); j <= p + k && j <= n; j++) {
            used[j] = 1;
        }
    }
    k = (2 * k + 1);
    int ans = 0;
    int last = 0;
    for (int i = 1; i <= n; i++) {
        if (used[i] == 0)
            continue;
        if (used[i] == 1) {
            ans += (i - 1 - last + k - 1) / k;
            last = i;
        }
    }
    ans += (n - last + k - 1) / k;
    cout << ans;
}	
 
int32_t main(int32_t argc, const char * argv[]) {
    cin.tie(0);
    cout.tie(0);
    ios_base::sync_with_stdio(0);
    // insert code here...
    int tt= 1;
    // std::cin >> tt;
	for (int t = 1; t <= tt; t++) {
		// cout << "Case #" << t << ": ";
        solve();
    }
    return 0;
}
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