Find the minimum number of length n, such that it is simultaneously divisible by some numbers(2,3,5,7)

#include < bits / stdc++.h>

#include <iostream>

using namespace std;

main()

{

    long long n;

    while(cin>>n)

    {

        if(n==1||n==2)

            cout<<"-1"<<endl;

        else

        {

            if(n==3)

            {

                cout<<210<<endl;

            }

            else

            {

                string s;

                long long i,k,k1=0,l,k2,k3;

                s='1';

                for(i=0;i<n-1;i++)

                    {

                        s+='0';

                    }

                    l=s.size();

                for(i=0;i<l;i++)

                {

                    k=k1*10+(s[i]-48);

                    k1=k%210;

                }

                k2=210-k1;

                k3=l-1;

                char ch;

                while(k2!=0)

                {

                    ch=k2%10;

                    s[k3]=ch+48;

                    k2/=10;

                    k3--;

                }

                cout<<s<<endl;

            }

        }

    }