#include <bits/stdc++.h>
using namespace std;
ifstream f("zombie.in");
ofstream g("zombie.out");
int n,d,k,i,j,a[1000005],v[1000005],cm[1000005];
int main()
{
    f>>d>>n>>k;
    for(i=1;i<=n;++i) f>>a[i];
    i=j=1;
    while(i<=n){
        while(a[i]-a[j]>d) ++j;
        v[i]=j;
        ++i;
    }
    cm[0]=0;
    for(i=1;i<=n;++i)
        cm[i]=min(cm[i-1]+1 , cm[v[i]-1]+k);
    //for(i=1;i<=n;++i) cout<<cm[i]<<' ';
    g<<cm[n];
    return 0;
}