#include <iostream>

using namespace std;

bool C[1000000010];

int main()
{
    int a,ab;
    cin>>a>>ab;
    int b;
    if (ab<500){
        b=ab;
    }
    else{
        b=500;
    }
    for (int i=2; i<=b; i++){
        if (C[i]==0) {
            for (int j=i+i; j<=b; j+=i){
                C[j]=1;
            }
        }
    }
    C[0]=1;
    C[1]=1;
    int s=0;
    for (int i=a; i<=b; i++){
        int n=i;
        int m=i;
        int w=0;
        int l=0;
        while (m){
            l++;
            m=m/10;
        }
        while(n){
            int c=0;
            int k=1;
            for (int z=1; z<=l; z++){
                k=k*10;
            }
            while (k>9){
                if (C[n%k]==1){
                    c=1;
                    break;
                }
                k=k/10;
            }
            if (c==1){
                w=1;
                break;
            }
            n=n/10;
        }
        if (w==0){
            //cout<<i<<endl;
            s++;
        }
    }
    cout<<s;
    return 0;
}