//-------------------------------------------AC code-------------------------------------------//

#include<cstdio>
#include<algorithm>
#include<cstring>

using namespace std;

const int MAXN = 30005;
const int MAXM = 100005;
int n, m, d, a, mon[MAXN];
int dp[MAXN][1001], ans;

inline int f(int x){
    return x - d + 255;
}

int main(){
//  freopen("pick.in", "r", stdin);
//  freopen("pick.out", "w", stdout);
    scanf("%d%d%d", &n, &m, &d);
    for(int i = 1; i <= m; i++)
        scanf("%d", &a), mon[a]++;
    memset(dp, 0xcf, sizeof dp);
    dp[d][f(d)] = mon[d];
    ans = mon[d]; 
    for(int i = d+1; i <= n; i++){
        for(int j = max(1, d-250); j <= min(i, d+250); j++){
            dp[i][f(j)] = max(dp[i-j][f(j-1)], max(dp[i-j][f(j)], dp[i-j][f(j+1)])) + mon[i];
            ans = max(ans, dp[i][f(j)]);
        }
    }
    printf("%d", ans);
    return 0;
}