import java.io.IOException;
import java.io.InputStream;
import java.io.PrintWriter;
import java.util.InputMismatchException;
import java.util.NoSuchElementException;

public class Main{

	static PrintWriter out;
	static InputReader ir;

	static void solve(){
		for(;;){
            int n=ir.nextInt();
            if(n==0)
                break;
            char[][] ap=new char[n][];
            String[] cd=new String[n];
            int ma=0;
            for(int i=0;i<n;i++){
            	ap[i]=ir.next().toCharArray();
            	cd[i]=Character.toString(ap[i][0]);
            	for(int j=0;j<ap[i].length-1;j++){
            		if(ap[i][j]=='a'||ap[i][j]=='i'||ap[i][j]=='u'||ap[i][j]=='e'||ap[i][j]=='o'){
            			cd[i]+=Character.toString(ap[i][j+1]);
            		}
            	}
            	ma=Math.max(ma,cd[i].length());
            }
            outer:
            for(int i=0;i<ma;i++){
            	for(int j=0;j<n;j++){
            		for(int k=j+1;k<n;k++){
            			if(code(cd[j],i+1).equals(code(cd[k],i+1))){
            				if(i==ma-1)
            					out.println(-1);
            				continue outer;
            			}
            		}
            	}
            	out.println(i+1);
            	break;
            }
        }
	}

	static String code(String s,int k){
		if(s.length()<=k) return s;
		return s.substring(0,k);
	}

	public static void main(String[] args) throws Exception{
		ir=new InputReader(System.in);
		out=new PrintWriter(System.out);
		solve();
		out.flush();
	}

	static class InputReader {

		private InputStream in;
		private byte[] buffer=new byte[1024];
		private int curbuf;
		private int lenbuf;

		public InputReader(InputStream in) {this.in=in; this.curbuf=this.lenbuf=0;}

		public boolean hasNextByte() {
			if(curbuf>=lenbuf){
				curbuf= 0;
				try{
					lenbuf=in.read(buffer);
				}catch(IOException e) {
					throw new InputMismatchException();
				}
				if(lenbuf<=0) return false;
			}
			return true;
		}

		private int readByte(){if(hasNextByte()) return buffer[curbuf++]; else return -1;}

		private boolean isSpaceChar(int c){return !(c>=33&&c<=126);}

		private void skip(){while(hasNextByte()&&isSpaceChar(buffer[curbuf])) curbuf++;}

		public boolean hasNext(){skip(); return hasNextByte();}

		public String next(){
			if(!hasNext()) throw new NoSuchElementException();
			StringBuilder sb=new StringBuilder();
			int b=readByte();
			while(!isSpaceChar(b)){
				sb.appendCodePoint(b);
				b=readByte();
			}
			return sb.toString();
		}

		public int nextInt() {
			if(!hasNext()) throw new NoSuchElementException();
			int c=readByte();
			while (isSpaceChar(c)) c=readByte();
			boolean minus=false;
			if (c=='-') {
				minus=true;
				c=readByte();
			}
			int res=0;
			do{
				if(c<'0'||c>'9') throw new InputMismatchException();
				res=res*10+c-'0';
				c=readByte();
			}while(!isSpaceChar(c));
			return (minus)?-res:res;
		}

		public long nextLong() {
			if(!hasNext()) throw new NoSuchElementException();
			int c=readByte();
			while (isSpaceChar(c)) c=readByte();
			boolean minus=false;
			if (c=='-') {
				minus=true;
				c=readByte();
			}
			long res = 0;
			do{
				if(c<'0'||c>'9') throw new InputMismatchException();
				res=res*10+c-'0';
				c=readByte();
			}while(!isSpaceChar(c));
			return (minus)?-res:res;
		}

		public double nextDouble(){return Double.parseDouble(next());}

		public int[] nextIntArray(int n){
			int[] a=new int[n];
			for(int i=0;i<n;i++) a[i]=nextInt();
			return a;
		}

		public long[] nextLongArray(int n){
			long[] a=new long[n];
			for(int i=0;i<n;i++) a[i]=nextLong();
			return a;
		}

		public char[][] nextCharMap(int n,int m){
			char[][] map=new char[n][m];
			for(int i=0;i<n;i++) map[i]=next().toCharArray();
			return map;
		}
	}
}

Measured memory_bytes: 38640