#include <iostream>
#include <iterator>
#include <vector>
#include <algorithm>
 
bool isNumber( const std::string& s )
{
    for( auto c : s )
    {
        if( !std::isdigit(c) ) return false;
    }
    return true;
}
 
int main() {
 
    std::istream_iterator<std::string> iit(std::cin);
    std::vector<std::string> v;
    std::copy_if( iit, std::istream_iterator<std::string>(), back_inserter(v), isNumber );
    std::ostream_iterator<std::string> oit( std::cout, "\n");
    std::copy( v.begin(), v.end(), oit );
 
	return 0;
}

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I have a 3 sons
and 1 son and 25dogs
end