#include<cstdio>
#include<cstring>
#include<algorithm>
#include<iostream>
using namespace std;
int n,A,B,P;
bool f[100010];
int father[10000];
int getfather(int u)
{
	if (father[u]==u)
		return u;
	return father[u]=getfather(father[u]);
}
void judge(int a,int b)
{
	int fa=getfather(a),fb=getfather(b);
	father[fb]=fa;
}
void generation(){
	n=100000;
	memset(f,true,sizeof(f));
	for (int i=2;i<=B;i++)
		if (f[i])
			for (int j=i+i;j<=B;j+=i){
					f[j]=false;
					if (i>=P)
						judge(i,j);
			}
}
int main()
{
	freopen("setb.in","r",stdin);
	freopen("setb.out","w",stdout);
	scanf("%d%d%d",&A,&B,&P);
	for (int i=1;i<=B;i++)
		father[i]=i;
	generation();
	memset(f,true,sizeof(f));
	int ans=0;
	for(int i=A;i<=B;i++)
	{
		int j=getfather(i);
		if (f[j])
		{
			f[j]=false;
			ans++;
		}
	}
	printf("%d",ans);
	return 0;
}