1094 - Google recruitment

#include
#include
#include
using namespace std;

int main()
{
int l,k,a,i,j;
cin >> l >> k;
string s;
cin >> s;
for(i = 0; i < (l-k+1); i++)
{
a = stoi(s.substr(i,k),0,10);
for(j = 2 ; j <= int(sqrt(a)); j++)
{
if(a%j==0)
{
break;
}
}
if(j == int(sqrt(a))+1){
cout << s.substr(i,k) <<endl;
break;
}
}
if(i>=(l-k+1)){
cout << “404” <<endl;
}
return 0;
}