Superprime Rib(usaco)

/* ID:tianlin2 PROG:sprime LANG:C++*/ #include <iostream>#include <fstream>#include <cmath>using namespace std;int n;ofstream fout("sprime.out");int isprm(int a){ if(a<2) return 0; int j=2; while(j<=sqrt((double)a)&&a%j!=0) ++j; if(j>sqrt((double)a)) return 1; return 0;}void find(int sum,int count){ if(count==n){fout<<sum<<endl;return;}for(int i=1;i<=9;++i){if(count>0&&(i%2==0||i==5)) continue;sum=sum*10+i;if(isprm(sum)) find(sum,count+1);sum=(sum-i)/10;}}int main(){ ifstream fin("sprime.in"); fin>>n; find(0,0); fout.close(); //system("pause"); return 0;}