Given two strings s1, s2 and K, find the of the longest subsequence by of at least length K.

Examples:

```Input : s1 = aggayxysdfa
s2 = aggajxaaasdfa
k = 4
Output : 8
Explanation: aggasdfa is the longest
subsequence that can be formed by taking
consecutive segments, minimum of length 4.
Here segments are "agga" and "sdfa" which
are of length 4 which is included in making
the longest subsequence.

Input : s1 = aggasdfa
s2 = aggajasdfaxy
k = 5
Output : 5

Input: s1 = "aabcaaaa"
s2 = "baaabcd"
k = 3
Output: 4
Explanation: "aabc" is the longest subsequence that
is formed by taking segment of minimum length 3.
The segment is of length 4.
```

Prerequisite : Longest Common Subsequence

Create a [][] array where i, j denotes the length of the longest common subsequence formed by characters of s1 till i and s2 till j having consecutive segments of at least length K. Create a cnt[][] array to count the length of the common segment. cnti, j= cnti-1, j-1+1 when s1[i-1]==s2[j-1]. If characters are not equal then segments are not equal hence mark cnti, j as 0.
When cnti, j>=k, then update the lcs value by adding the value of cnti-a, j-a where a is the length of the segments a<=cnti, j. The answer for the longest subsequence with consecutive segments of at least length k will be stored in lcs[n][m] where n and m are the length of string1 and string2.

```// CPP program to find the Length of Longest
// subsequence formed by consecutive segments
// of at least length K
#include <bits/stdc++.h>
using namespace std;

// Returns the length of the longest common subsequence
// with a minimum of length of K consecutive segments
int longestSubsequenceCommonSegment(int k, string s1,
string s2)
{
// length of strings
int n = s1.length();
int m = s2.length();

// declare the lcs and cnt array
int lcs[n + 1][m + 1];
int cnt[n + 1][m + 1];

// initialize the lcs and cnt array to 0
memset(lcs, 0, sizeof(lcs));
memset(cnt, 0, sizeof(cnt));

// iterate from i=1 to n and j=1 to j=m
for (int i = 1; i <= n; i++) {
for (int j = 1; j <= m; j++) {

// stores the maximum of lcs[i-1][j] and lcs[i][j-1]
lcs[i][j] = max(lcs[i - 1][j], lcs[i][j - 1]);

// when both the characters are equal
// of s1 and s2
if (s1[i - 1] == s2[j - 1])
cnt[i][j] = cnt[i - 1][j - 1] + 1;

// when length of common segment is
// more than k, then update lcs answer
// by adding that segment to the answer
if (cnt[i][j] >= k) {

// formulate for all length of segments
// to get the longest subsequence with
// consecutive Common Segment of length
// of min k length
for (int a = k; a <= cnt[i][j]; a++)

// update lcs value by adding segment length
lcs[i][j] = max(lcs[i][j],
lcs[i - a][j - a] + a);

}
}
}

return lcs[n][m];
}

// driver code to check the above fucntion
int main()
{
int k = 4;
string s1 = "aggasdfa";
string s2 = "aggajasdfa";
cout << longestSubsequenceCommonSegment(k, s1, s2);
return 0;
}
```

Output:

```8
```

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