#include<bits/stdc++.h>
using namespace std;
const int N=1e5+5;
int a,b,p,ans;
int fa[N],np[N];
int find(int x){
	return x==fa[x]?x:fa[x]=find(fa[x]);
}
int main(){
	freopen("setb.in","r",stdin);
	freopen("setb.out","w",stdout);
	scanf("%d%d%d",&a,&b,&p);
	ans=b-a+1;
	for(int i=a;i<=b;++i) fa[i]=i;
	for(int i=2;i<=b;++i){
		if(!np[i]){
			if(i>=p){
				for(int j=i*2;j<=b;j+=i){
					np[j]=true;
					if(j-i>=a&&find(j)!=find(j-i)){
						fa[find(j)]=find(j-i);
						--ans;
					}
				}
			}else{
				for(int j=i*2;j<=b;j+=i){
					np[j]=true;
				}
			}
		}
	}
	printf("%d\n",ans);
	return 0;
}