import java.util.Scanner;
import java.util.Set;
import java.util.TreeSet;

public class search {
	static int[][] paths;

	public static void main(String[] args) {
		Scanner in = new Scanner(System.in);
		int sites, officers, pathnum;
		while ((sites = in.nextInt()) != 0) {
			officers = in.nextInt();
			pathnum = in.nextInt();
			paths = new int[sites][sites];
			for (int i = 0; i < sites; i++) {
				for (int j = 0; j < sites; j++) {
					paths[i][j] = Integer.MAX_VALUE / 3;
				}
			}
			for (int i = 0; i < pathnum; i++) {
				String path = in.next();
				paths[path.charAt(0) - 'A'][path.charAt(1) - 'A'] = 1;
				paths[path.charAt(1) - 'A'][path.charAt(0) - 'A'] = 1;
			}
			for (int k = 0; k < sites; k++) {
				for (int i = 0; i < sites; i++) {
					for (int j = 0; j < sites; j++) {
						int cur = paths[i][j];
						int nuu = paths[i][k] + paths[j][k];
						if (nuu < cur) paths[i][j] = nuu;
					}
				}
			}
			int[] locs = new int[officers];
			for (int i = 0; i < officers; i++) locs[i] = 0;
			Set<Integer> visited = new TreeSet<Integer>();
			visited.add(0);
			int[] times = new int[officers];
			while (visited.size() < sites) {
				for (int i = 0; i < officers; i++) {
					int closest = getClosest(paths, locs[i], visited);
					if (closest == 9001) closest = getClosest2(paths, locs[i]);
					times[i] += paths[locs[i]][closest]; 
					locs[i] = closest;
					visited.add(closest);
				}
			}
			int min = 9999;
			for (int i = 0; i < officers; i++) {
				if (times[i] < min) min = times[i];
			}
			System.out.println(min);
		}
	}
	
	public static int getClosest(int[][] map, int start, Set<Integer> invalid) {
		int min = 9001;
		int spot = 9001;
		for (int i = 0; i < map[0].length; i++) {
			if (invalid.contains(i)) continue;
			if (map[start][i] < min) {
				min = map[start][i];
				spot = i;
			}
		}
		return spot;
	}
	
	public static int getClosest2(int[][] map, int start) {
		int min = 9002;
		int spot = 9002;
		for (int i = 0; i < map[0].length; i++) {
			if (map[start][i] < min) {
				min = map[start][i];
				spot = i;
			}
		}
		return spot;
	}
	
}