#include <iostream>
#include <boost/algorithm/string/find.hpp>
 
using namespace std;
using namespace boost;
 
int main() {
 
    string a = "The rain in Spain falls mainly on the plain";
 
    iterator_range<string::iterator> r = find_nth(a,"ain",2);
    cout << distance(a.begin(),r.begin()) << endl;
 
    return 0;
}