#include<stdio.h>
#include<iostream>
#include<string.h>

using namespace std;

bool check (string a, string b)
{
    int l1,l2,i;
    
    l1=a.size();
    l2=b.size();
    
    if(l1<=l2)
    {
        for(i=0;i<l1;i++)
        {
            if(a[i]<b[i])return 1;
            if(b[i]<a[i])return 0;
        }
        
        return 1;
    }
    else
    {
        for(i=0;i<l2;i++)
        {
            if(a[i]<b[i])return 1;
            if(b[i]<a[i])return 0;
        }
        
        return 0;
    }
}

int main ()
{
    freopen ("phonebook.in", "r", stdin);
    freopen ("phonebook.out", "w", stdout);
    
    int n,i,res=-1;
    string a,b;
    
    cin>>n>>a;
    
    for(i=1;i<n;i++)
    {
        cin>>b;
        if(res==-1)
        {
            if(check(a,b)==0)
            {
                res=i;
            }
        }
        
        a=b;
    }
    
    cout<<res<<endl;
    
    return 0;
}