import java.util.Scanner;

public class EvenTree {

public static void main(String[] args) {

Scanner in = new Scanner(System.in);

int nodes = in.nextInt();

int vertices = in.nextInt();

int weightChange;

int[] graph = new int[nodes + 1];

int[] weight = new int[nodes + 1];

for (int i = 0; i < nodes + 1; i++) {

graph[i] = 0;

weight[i] = 1;

}

for (int i = 0; i < vertices; i++) {

int node = in.nextInt();

int parent = in.nextInt();

weightChange = weight[node];

graph[node] = parent;

while (graph[node] != 0) {

weight[graph[node]] += weightChange;

node = graph[node];

}

}

int cutOff = 2;

int cuts = 0;

int parent;

int maxWeight = 0;

for (int i = 0; i < weight[i]; i++) {

maxWeight = (weight[i] > maxWeight ? weight[i] : maxWeight);

}

int oldCuts = -1;

while (cuts != oldCuts) {

oldCuts = cuts;

while (cutOff < maxWeight) {

for (int i = 0; i < vertices; i++) {

if (weight[i] == cutOff) {

cuts += 1;

weightChange = weight[i];

parent = i;

while (graph[parent] != 0) {

weight[parent] -= weightChange;

parent = graph[parent];

}

graph[i] = 0;

}

}

cutOff += 2;

}

cutOff = 2;

}

System.out.println(cuts);

in.close();

}

}