#include<cstdio>
using namespace std;
int fa[100005],a,b,p,st,prime[100005],cnt;
bool vis[100005];
int t[100005];
int Find(int x){
    if(fa[x]==x)return x;
    return fa[x]=Find(fa[x]);
}
int main(){
    freopen("setb.in","r",stdin);
    freopen("setb.out","w",stdout);
    for(int i=2;i<=100000;i++){
        if(!vis[i]){
            prime[++cnt]=i;
        }
        for(int j=1;j<=cnt&&i*prime[j]<=100000;j++){
            vis[i*prime[j]]=1;
            if(i%prime[j]==0)break;
        }
    }
    scanf("%d%d%d",&a,&b,&p);
    for(int i=1;i<=b;i++)fa[i]=i;
    while(prime[++st]<p); 
    for(int i=a;i<=b;i++){
        for(int j=st;j<=cnt;j++){
            if(i%prime[j]==0){
                for(int k=i/prime[j]+1;k*prime[j]<=b;k++){
                    fa[Find(k*prime[j])]=Find(i);
                }
            }
        }
    }
    int ans=0;
    for(int i=a;i<=b;i++){
        t[Find(i)]++;
    }
    for(int i=a;i<=b;i++){
        if(t[i])ans++;
    }
    printf("%d",ans);
    return 0;
}