C :

#include<stdio.h>
#include<stdlib.h>
#include<string.h>
#include<ctype.h>
#include<math.h>
char r[1001],t[1];
int main(){
	char s[1001];
	scanf("%s",&s);
	if(s=="0"){
		printf("%d",0);
		return 0;
	}
	long long m = 0,x,sum=0;
	int n = strlen(s),i,j;
	for(i=0;i<n;i++){
		x = s[i] - '0';
		for(j=1;j<=n-i-1;j++){
			x = x * 2;
		}
		sum = sum + x;
	} 
	while(sum!=0){
		t[0] = sum%8+'0';
		strcat(r,t);
		sum = sum/8;
	}
	for(i=strlen(r)-1;i>=0;i--){
		printf("%c",r[i]);
	}
	return 0;
}

C++ :

#include<bits/stdc++.h>
using namespace std;
char f(string s) {
	int r=0,i,t=1;
	char s1;
	for (i=s.size()-1;i>=0;i--) {
		r=r+(s[i]-48)*t;
		t*=2;
	}
	s1=r+48;
	return s1;
}
int main(){
	string s,t;
	cin>>s;
	int i,x;
	x=s.size();
	if (s.size()%3!=0) {
		for (i=1;i<=3-(x%3);i++) {
			s="0"+s;
		}
	}
	for (i=0;i<s.size();i+=3) {
		t=s.substr(i,3);
		cout<<f(t);
	}
	cout<<endl;

	return 0;
}

Python :

n=input()
a=int(n,2)
b=oct(a)[2:]
print(b)