USACO-section1.5 Prime Palindromes[回文数][素数]

/*
ID:jsntrdy1
PROG:pprime
LANG: C++
*/
#include<cstdio>
#include<iostream>
#include<cstring>
#include<fstream>
#include<cmath>
bool c[10000000];
using namespace std;
ifstream fin("pprime.in");
ofstream fout("pprime.out");

int main()
{
int k,j,a,b,i;
fin>>a>>b;
if (b>9999999) b=9999999;
for (i=2;i<=int(sqrt(b));i++)
if (!c[i])
for (j=i*i;j<=b;j=j+i)
c[j]=1;
for (i=a;i<=b;i++){
k=i;j=0;
while (k){
j=j*10+k%10;
k=k/10;
}
if ((!c[i])&&(i==j))
fout<<i<<endl;
}
fin.close();
fout.close();
return 0;
}