//20230929 @ Luogu.com.cn
#include<bits/stdc++.h>
using namespace std;
int a,b,p,prime[100005],t,f[100005],ppos=1e9,ans;
bool isprime[100005];

int find(int x)
{
	if(f[x]!=x)f[x]=find(f[x]);
	return f[x];
}

void unite(int x,int y)
{
	x=find(x);y=find(y);
	f[x]=y;
}

signed main()
{
	ios::sync_with_stdio(0);cin.tie(0);cout.tie(0);
//	freopen("1.txt","r",stdin);
	cin>>a>>b>>p;
	
	isprime[0]=isprime[1]=true;
    for(long long i=2;i<=b;i++)
        if(!isprime[i])
        {
            t++;
            prime[t]=i;
            for(long long j=i*i;j<=b;j+=i)
                isprime[j]=true;
        }
    
    for(int i=a;i<=b;i++)f[i]=i;
    
    for(int i=1;i<=t;i++)
    {
    	if(prime[i]>=p)
    	{
    		for(int j=1;j<=b;j++)
    		{
    			if(j*prime[i]>b)break;
    			unite(prime[i],j*prime[i]);
			}
		}
	}

	for(int i=a;i<=b;i++)
	{
		if(f[i]==i)ans++;
	}
	
	cout<<ans;
	return 0;
}