C++ :

#include<iostream>
#include<algorithm>
using namespace std;
int fd[30005],sum[30005];
int f(int x){
	while(fd[x]!=x) x=fd[x];
	return x;
}
int main(){
	int n,m,k1,k2,x,y;
	cin>>n>>m;
	for (int i=1;i<=n;i++) fd[i]=i;
	for (int i=1;i<=m;i++){
		cin>>x>>y;
		k1=f(x);
		k2=f(y);
		if (k1!=k2) fd[k2]=fd[x]=fd[y]=k1; 
	}
	for (int i=1;i<=n;i++)
		sum[f(fd[i])]++;
	int ans=0;
	for (int i=1;i<=n;i++)
		ans=max(ans,sum[i]);
	cout<<ans;
	return 0;
}

Python :

# coding=utf-8
import sys

class UnionFind:
    def __init__(self, size):
        self.parent = [i for i in range(size)]
        self.rank = [0] * size
        self.size = [1] * size  # Initialize the size for each component
        self.max_size = 1

    def find(self, node):
        if self.parent[node] != node:
            self.parent[node] = self.find(self.parent[node])  # Path compression
        return self.parent[node]

    def union(self, node1, node2):
        root1 = self.find(node1)
        root2 = self.find(node2)

        if root1 != root2:
            if self.rank[root1] < self.rank[root2]:
                self.parent[root1] = root2
                self.size[root2] += self.size[root1]
                self.max_size = max(self.max_size, self.size[root2])
            elif self.rank[root1] > self.rank[root2]:
                self.parent[root2] = root1
                self.size[root1] += self.size[root2]
                self.max_size = max(self.max_size, self.size[root1])
            else:
                self.parent[root2] = root1
                self.rank[root1] += 1
                self.size[root1] += self.size[root2]
                self.max_size = max(self.max_size, self.size[root1])

def main():
    # Read the first line of input
    n, m = map(int, sys.stdin.readline().split())
    uf = UnionFind(n + 1)  # Initialize UnionFind with one extra space for 1-indexed input

    # Process each friend pair
    for _ in range(m):
        a, b = map(int, sys.stdin.readline().split())
        uf.union(a, b)

    # Output the size of the largest friend group
    print(uf.max_size)

if __name__ == "__main__":
    main()