import core.bitop, std.algorithm, std.ascii, std.bigint, std.conv, std.math,
    std.functional, std.numeric, std.range, std.stdio, std.string, std.random,
    std.typecons, std.container, std.format, std.datetime;

// dfmt off
T lread(T = long)(){return readln.chomp.to!T();}
T[] lreads(T = long)(long n){return generate(()=>readln.chomp.to!T()).take(n).array();}
T[] aryread(T = long)(){return readln.split.to!(T[])();}
void scan(TList...)(ref TList Args){auto line = readln.split();
foreach (i, T; TList){T val = line[i].to!(T);Args[i] = val;}}
alias sread = () => readln.chomp();enum MOD = 10 ^^ 9 + 7;
alias PQueue(T, alias less = "a<b") = BinaryHeap!(Array!T, less);
// dfmt on

void main()
{
    long N, M;
    scan(N, M);
    auto cnt = new long[](N);
    cnt[] = 1;
    auto red = new bool[](N);
    red[0] = true;
    foreach (_; 0 .. M)
    {
        long X, Y;
        scan(X, Y);
        X--, Y--;
        red[Y] = red[X] || red[Y];
        red[X] = (1 != cnt[X]) && red[X];
        cnt[X]--;
        cnt[Y]++;
    }
    red.sum().writeln();
}
