#include<stdio.h>
using namespace std;
int n,d,k,i,lim,a[1000002],v[1000002];
int main()
{
freopen("zombie.in","r",stdin);
freopen("zombie.out","w",stdout);
scanf("%d",&d);
scanf("%d",&n);
scanf("%d",&k);
v[0]=0;
lim=1;
for(i=1;i<=n;i++)
{
	scanf("%d",&a[i]);
	v[i]=v[i-1]+17;
	while(a[lim]<a[i]-d+1)
		lim++;
	if(v[i]>v[lim-1]+k) v[i]=v[lim-1]+k;
}
printf("%d",v[n]);
return 0;
}