接龙队列 线性dp
n = int(input()) a,dp = [0]*100005,[0]*100005 temp = list(map(str,input().split())) for i in range(n): a[i] = temp[i] for i in range(n): x,y = int(a[i][0]),int(a[i][-1]) dp[y] = max(dp[x]+1,dp[y]) print(n-max(dp))