#include <stdio.h>
int p[50001]={0};
void sieve(){
int i,j,k;
for(i=1;i<159;++i)
   if(!p[i])
     for(k=(i<<1)+1,j=i*k+i;j<50000;j+=k)
      p[j]=1;
for(p[0]=i=1;i<50001;++i)p[i]=p[i-1]+1-p[i];}

int main(){
int a,b;
sieve();
while(scanf("%d%d",&a,&b),a!=-1||b!=-1)
printf("%d\n",(b<2?0:p[(b-1)>>1])-(a<3?0:p[(a>>1)-1]));
return 0;}