#include <iostream>
using namespace std;

int dp[30][30];
int maxlen;    /* 記錄最大公共子串長度 */
int maxindex;  /* 記錄最大公共子串在串1的起始位置 */

void LCS(char * X, int xlen, char * Y, int ylen)
{
	maxlen = maxindex = 0;
	for(int i = 0; i < xlen; ++i)
	{
		for(int j = 0; j < ylen; ++j)
		{
			if(X[i] == Y[j])
			{
				if(i && j)
				{
					dp[i][j] = dp[i-1][j-1] + 1;
				}
				if(i == 0 || j == 0)
				{
					dp[i][j] = 1;
				}
				if(dp[i][j] > maxlen)
				{
					maxlen = dp[i][j];
					maxindex = i + 1 - maxlen;
				}
			}
		}
	}
	for (int i = 0; i < maxlen; i++)
	{
		printf("%c", X[maxindex+i]);
	}
	printf("\n");
}

int main()
{
	char X[] = "aaaba";
	char Y[] = "abaa";
	LCS(X,strlen(X),Y,strlen(Y));
	return 0;
}