Convertir un número binario a base octal

nclude <iostream>
#include <string>
using namespace std;

int bin2oct(string bin);

int main()
{
    string bin;
    cin >> bin;
    cout << bin2oct(bin) << endl;
    return 0;
}

int bin2oct(string bin)
{
    int oct = 0;
    for (int i = 0; i < bin.size(); i++