>>83
#include <iostream>
#include <fstream>
main()
{
int n;
std::ifstream ifs("abc.txt");
if(!ifs){
std::cerr << "file open error" << std::endl;
}
ifs >> n;
ifs.close();
std::ofstream ofs("abc.txt");
ofs << (n + 1) << std::ends;
}