Language: C++

[15:25, 8/4/2020] Kamal: #include<bits/stdc++.h>
using namespace std;

typedef long long int lli;
typedef vector<lli> vlli;

#define IOS ios::sync_with_stdio(0); cin.tie(0); cout.tie(0)
#define IO freopen("in.txt","r",stdin); freopen("out.txt","w",stdout)
#define pb push_back  
#define pf push_front
#define ub upper_bound 
#define lb lower_bound
#define bs binary_search
#define mp make_pair
#define F first
#define S second
#define plli pair<lli,lli>
#define all(a) (a).begin(),(a).end() 
#define PI 3.141592653589793238
#define mod 1000000007
char nn = '\n';

lli temp,arr[1000005],fk,sk;

lli firstdig(lli a)
{
	lli x=log(a)/log(10);
	lli y=a/pow(10,x);
	return y;
}

lli findsize(lli a)
{
	lli x=log(a)/log(10)+1;
	return x;
}

lli findnum(lli a,lli b)
{
	lli x;
	x=a*pow(10,b)+arr[b];
	…
[15:25, 8/4/2020] Kamal: submit krke dekhio zara
[17:06, 8/4/2020] Sujal: Wait
[18:32, 8/4/2020] Sujal: bhai ek case me galat a ra
[18:32, 8/4/2020] Sujal: wa
[18:43, 8/4/2020] Kamal: Acha dekhta hu
[18:43, 8/4/2020] Kamal: Case mil sakta h kya?
[19:19, 8/4/2020] Kamal: #include<bits/stdc++.h>
using namespace std;

typedef long long int lli;
typedef vector<lli> vlli;

#define IOS ios::sync_with_stdio(0); cin.tie(0); cout.tie(0)
#define IO freopen("in.txt","r",stdin); freopen("out.txt","w",stdout)
#define pb push_back  
#define pf push_front
#define ub upper_bound 
#define lb lower_bound
#define bs binary_search
#define mp make_pair
#define F first
#define S second
#define plli pair<lli,lli>
#define all(a) (a).begin(),(a).end() 
#define PI 3.141592653589793238
#define mod 1000000007
char nn = '\n';

lli temp,arr[1000005],fk,sk,k;

lli firstdig(lli a)
{
	lli x=log(a)/log(10);
	lli y=a/pow(10,x);
	return y;
}

lli findsize(lli a)
{
	lli x=log(a)/log(10)+1;
	return x;
}

lli findnum(lli a,lli b)
{
	lli x;
	x=a*pow(10,b)+arr[b];
	return x;
}

lli finddig(lli a)
{
	lli c;
	if(a!=0)
	{
		lli fa=firstdig(a),sa=findsize(a); 
		if(fa>fk) c=sk-sa;
		else c=sk-sa+1;
	}
	else
	{
		if(7>=fk) c=sk;
		else c=sk+1;
	}
	temp=findnum(a,c);
	if(temp<k) temp=findnum(temp,1);
	return c;
}

int main()	 	
{	
	IOS;		
	#ifndef  ONLINE_JUDGE
	IO;
	#endif
	lli t=1,i,h,n;
	bool f=true;
	string str;

	arr[1]=7;
	for(i=2;i<1000005;i++) arr[i]=arr[i-1]*10+7;
	lli c=0,rem=-1;
	set<lli> s;
	cin>>k;
	fk=firstdig(k);
	sk=findsize(k);
	//cout<<fk<<" "<<sk<<nn;
	lli p=finddig(0);
	//cout<<p<<" "<<temp<<nn;
	while(rem!=0 && s.find(rem)==s.end())
	{
		c+=p;
		s.insert(rem);
		rem=temp%k;
		p=finddig(rem);
		//cout<<temp<<" "<<rem<<nn;
	}
	if(rem!=0) cout<<-1<<nn;
	else cout<<c<<nn;
	return 0;	
}

Compiler output:
a.cc:1:26: error: stray '#' in program
    1 | [15:25, 8/4/2020] Kamal: #include<bits/stdc++.h>
      |                          ^
a.cc:42:9: error: extended character … is not valid in an identifier
   42 |         …
      |         ^
a.cc:49:26: error: stray '#' in program
   49 | [19:19, 8/4/2020] Kamal: #include<bits/stdc++.h>
      |                          ^
a.cc:1:1: error: expected unqualified-id before '[' token
    1 | [15:25, 8/4/2020] Kamal: #include<bits/stdc++.h>
      | ^
a.cc:5:9: error: 'vector' does not name a type
    5 | typedef vector<lli> vlli;
      |         ^~~~~~
a.cc: In function 'lli firstdig(lli)':
a.cc:27:15: error: 'log' was not declared in this scope; did you mean 'long'?
   27 |         lli x=log(a)/log(10);
      |               ^~~
      |               long
a.cc:28:17: error: 'pow' was not declared in this scope
   28 |         lli y=a/pow(10,x);
      |                 ^~~
a.cc: In function 'lli findsize(lli)':
a.cc:34:15: error: 'log' was not declared in this scope; did you mean 'long'?
   34 |         lli x=log(a)/log(10)+1;
      |               ^~~
      |               long
a.cc: In function 'lli findnum(lli, lli)':
a.cc:41:13: error: 'pow' was not declared in this scope
   41 |         x=a*pow(10,b)+arr[b];
      |             ^~~
a.cc:42:9: error: '\U00002026' was not declared in this scope
   42 |         …
      |         ^
a.cc:43:4: error: expected ']' before ':' token
   43 | [15:25, 8/4/2020] Kamal: submit krke dekhio zara
      |    ^
      |    ]
a.cc:53:9: error: 'vector' does not name a type
   53 | typedef vector<lli> vlli;
      |         ^~~~~~
a.cc:74:1: error: a function-definition is not allowed here before '{' token
   74 | {
      | ^
a.cc:81:1: error: a function-definition is not allowed here before '{' token
   81 | {
      | ^
a.cc:87:1: error: a function-definition is not allowed here before '{' token
   87 | {
      | ^
a.cc:94:1: error: a function-definition is not allowed here before '{' token
   94 | {
      | ^
a.cc:112:9: warning: empty parentheses were disambiguated as a function declaration [-Wvexing-parse]
  112 | int main()
      |         ^~
a.cc:112:9: note: remove parentheses to default-initialize a variable
  112 | int main()
      |         ^~
      |         --
a.cc:112:9: note: or replace parentheses with braces to value-initialize a variable
a.cc:113:1: error: a function-definition is not allowed here before '{' token
  113 | {
      | ^
a.cc:143:2: error: expected '}' at end of input
  143 | }
      |  ^
a.cc:39:1: note: to match this '{'
   39 | {
      | ^
a.cc:143:2: warning: no return statement in function returning non-void [-Wreturn-type]
  143 | }
      |  ^