#include <iostream>
#include <cmath>
using namespace std;
int tongChuSo ( int n ){
int sum = 0;
while( n>0){
sum += n % 10;
n /= 10;
}
return sum;
}
bool snt( int n ){
if(n < 2) return 0;
for(int i=2 ; i<=sqrt(n) ; i++){
if(n % i == 0) return 0;
}
return 1;
}
int main() {
int l , r;
cin>>l>>r;
int ans=0;
for(int i=l+1;i<r;i++){
if(snt(tongChuSo(i))) ans++;
}
cout<<ans<<endl;
return 0;
}
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