#pragma comment(linker, "/STACK:102400000, 102400000")

#include<cstdio>

#include<cstring>

#include<cstdlib>

#include<cctype>

#include<cmath>

#include<iostream>

#include<sstream>

#include<iterator>

#include<algorithm>

#include<string>

#include<vector>

#include<set>

#include<map>

#include<stack>

#include<deque>

#include<queue>

#include<list>

#define Min(a, b) ((a < b) ? a : b)

#define Max(a, b) ((a < b) ? b : a)

const double eps = 1e-8;

inline int dcmp(double a, double b){

    if(fabs(a - b) < eps) return 0;

    return a > b ? 1 : -1;

}

typedef long long LL;

typedef unsigned long long ULL;

const int INT_INF = 0x3f3f3f3f;

const int INT_M_INF = 0x7f7f7f7f;

const LL LL_INF = 0x3f3f3f3f3f3f3f3f;

const LL LL_M_INF = 0x7f7f7f7f7f7f7f7f;

const int dr[] = {0, 0, -1, 1, -1, -1, 1, 1};

const int dc[] = {-1, 1, 0, 0, -1, 1, -1, 1};

const int MOD = 1e9 + 7;

const double pi = acos(-1.0);

const int MAXN = 100 + 10;

const int MAXT = 10000 + 10;

using namespace std;

int a[MAXN][MAXN];

int ans;

int N, M;

int solve(){

    for(int i = 1; i <= N; ++i){

        int cntfront = 0, cntrear = 0;

        for(int j = 1; j <= N; ++j){

            if(a[j][i]) ++cntfront;

            if(a[i][j]) ++cntrear;

        }

        if(cntfront + cntrear == N - 1) ++ans;

    }

    return ans;

}

int main(){

    scanf("%d%d", &N, &M);

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

        int u, v;

        scanf("%d%d", &u, &v);

        a[u][v] = 1;

    }

    for(int k = 1; k <= N; ++k){

        for(int i = 1; i <= N; ++i){

            for(int j = 1; j <= N; ++j){

                if(a[i][k] && a[k][j]) a[i][j] = 1;

            }

        }

    }

    printf("%d\n", solve());

    return 0;

}