COdeforce - Phone numbers

#include<bits/stdc++.h>
using namespace std;
#define fast()(ios_base::sync_with_stdio(false),cin.tie(NULL));
typedef long long ll;
int main()
{
    fast();
    int i,n;
    cin>>n;
    string s;
    cin>>s;
    if(n%2==0)
    {
        i=2;
        cout<<s[0]<<s[1];
    }
    else
    {
        i=3;
        cout<<s[0]<<s[1]<<s[2];
    }
    for(i;i<n;i+=2)
    {
        cout<<"-"<<s[i]<<s[i+1];
    }
    cout<<endl;
    //printf("\n");
    return 0;
}