#include<bits/stdc++.h>
using namespace std;
int a,b,P,ans;
int fa[100005];
int p[100005];
int find(int x){
    if(fa[x]==x) return x;
    return find(fa[x]);
}
void fp(int k){
    if(k>=100005) return ;
    for(int j=2;j<=100005/k;j++){
        p[k*j]=0;
    }
    int nxt=k+1;
    while(p[nxt]==0){
        nxt++;
    }
    fp(nxt);
}
int f(int x,int y){
    if(y<x) swap(x,y);
    for(int i=x;i>=1;i--){
        if(x%i==0&&y%i==0&&p[i]){
            return i;
        }
    }
}
int main(){
    freopen("setb.in","r",stdin);
    freopen("setb.out","w",stdout);
    cin>>a>>b>>P;
    for(int j=1;j<=100005;j++) p[j]=1;
    fp(2);
    ans=b-a+1;
    for(int i=a;i<=b;i++){
        fa[i]=i;
    }
    for(int i=a;i<=b;i++){
        for(int j=i+1;j<=b;j++){
            int fi=find(i);
            int fj=find(j);
            if(fi==fj) continue;
            if(f(i,j)>=P){
                fa[fj]=fi;
                //cout<<i<<" "<<j<<"\n";
                ans--;
            }
        }
    }
    cout<<ans;
    return 0;
}