//20 100000 23
//12400
#include<bits/stdc++.h>
using namespace std;
int a,b,p,ans,vis[100001],f[100001];
int get(int x){
    while(x!=f[x]) x=f[x];
    return x;
}
int main(){
    freopen("setb.in","r",stdin);
    freopen("setb.out","w",stdout);
    cin>>a>>b>>p;
    ans=b-a+1;
    for(int i=a;i<=b;i++) f[i]=i;
    for(int i=2;i<=b;i++){
        if(vis[i]==0){
            for(int j=i*2;j<=b;j+=i){
                vis[j]=1;
                if(i>=p&&j-i>=a&&get(j)!=get(j-i)){
                    ans--;
                    f[get(j)]=get(j-i);
                }
            }
        }
    }
    cout<<ans<<endl;
    return 0;
}