1
 2
 3
 4
 5
 6
 7
 8
 9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
#include <iostream>
#include <vector>
#include <algorithm>
using namespace std;

vector<vector<int> > edges;
vector<int> blacklist;
vector<int> vis;

void dfs(int node) {
    if (blacklist[node]) {
        vis[node] = 0;
        return;
    }
    if (vis[node]!=-1)return;
    int res = 1;
    for (int c:edges[node]) {
        dfs(c);
        res = max(res, vis[c]+1);
    }
    vis[node] = res;
}

int main() {
    int n,m,k;
    cin >> n >> m >> k;
    edges.resize(n);
    blacklist.resize(n);
    for (int i=0; i < k; i++) blacklist[i] = 1;
    vis.resize(n);

    for (int i=0; i < m; i++) {
        int a,b;
        cin >> a >> b;
        edges[a-1].push_back(b-1);
    }

    int res = 1e9;
    int iter = 30*1000*1000 / (n+m);
    //cerr << iter << endl;

    for (int i=0; i < iter; i ++) {
        random_shuffle(blacklist.begin(), blacklist.end());
        for (int&v:vis)v=-1;

        for (int j=0; j < n; j++)
            dfs(j);

        int nres = *max_element(vis.begin(), vis.end());
        res = min(res, nres);
    }
    cout << res << endl;

}