#include <fstream>
using namespace std;
long long v[1000005];
int main()
{
	ifstream f("zombie.in");
	ofstream g("zombie.out");
	int D,N,K,i,max,chakra,x;
	f>>D; f>>N; f>>K; chakra=0;
	for(i=1;i<=N;i++) f>>v[i];
	i=2;
	x=v[1];
	while(i<=N)
	{   max=1;
		while(v[i]-x+1<D&&i<=N) 
			{max++; i++;}
		if(max>=K) chakra=chakra+K;
		else chakra=chakra+max;
		x=v[i];
		i++;
	}
	g<<chakra;
	f.close();
	g.close();
	return 0;
}