#include<bits/stdc++.h>
using namespace std;
int prime[1000050],check[1000050],cnt,fa[1000050],a,b,p,ans;
void oula(int n)
{
	check[1]=1;
	for(int i=2;i<=n;i++)
	{
		if(check[i]==0)prime[++cnt]=i;
		for(int j=1;j<=cnt&&prime[j]*i<=n;j++)
		{
			check[prime[j]*i]=1;
			if(i%prime[j]==0)break;
		}
	}
}
int find(int k)
{
	if(fa[k]==k)return k;
	return fa[k]=find(fa[k]);
}
int main()
{
	freopen("setb.in","r",stdin);
	freopen("setb.out","w",stdout);
	cin>>a>>b>>p;
	oula(b);
	for(int i=a;i<=b;i++)fa[i]=i;
	for(int i=p;i<=b;i++)
	{
		if(check[i]==0)
		{
			int c=a/i*i;
			if(c!=a)c+=i;
			for(int j=c;j<=b/i*i+i&&j<=b;j+=i)
			{
				fa[find(j)]=find(c);
			}
		}
	}
	for(int i=a;i<=b;i++)
	{
		if(fa[i]==i)ans++;
		//cout<<fa[i]<<endl;
	}
	cout<<ans;
	return 0;
}