#include <bits/stdc++.h> using namespace std; using ll = long long; long long readInt(long long l,long long r,char endd){ long long x=0; int cnt=0; int fi=-1; bool is_neg=false; while(true){ char g=getchar(); if(g=='-'){ assert(fi==-1); is_neg=true; continue; } if('0'<=g && g<='9'){ x*=10; x+=g-'0'; if(cnt==0){ fi=g-'0'; } cnt++; assert(fi!=0 || cnt==1); assert(fi!=0 || is_neg==false); assert(!(cnt>19 || ( cnt==19 && fi>1) )); } else if(g==endd){ if(is_neg){ x= -x; } assert(l<=x && x<=r); return x; } else { assert(false); } } } string readString(int l,int r,char endd){ string ret=""; int cnt=0; while(true){ char g=getchar(); assert(g!=-1); if(g==endd){ break; } cnt++; ret+=g; } assert(l<=cnt && cnt<=r); return ret; } long long readIntSp(long long l,long long r){ return readInt(l,r,' '); } long long readIntLn(long long l,long long r){ return readInt(l,r,'\n'); } string readStringLn(int l,int r){ return readString(l,r,'\n'); } string readStringSp(int l,int r){ return readString(l,r,' '); } long long P10(int x){ return x == 0 ? 1 : 10 * P10(x - 1); } template <typename T, typename R = long long> vector<T> readArr(int len, R l, R r){ vector<T> a(len); for(int i = 0; i < len; i++){ if(i + 1 < len){ a[i] = readIntSp(l, r); } else { a[i] = readIntLn(l, r); } } return a; } int main(){ int t = readIntLn(1, 5 * P10(4)); int sum_nm = 0; while(t--){ int n = readIntLn(1, 2 * P10(5)); int m = readIntLn(0, min(1ll * n * (n - 1), 4 * P10(5))); sum_nm += n + m; vector<int> in(n), out(n), ord; vector<vector<int>> adj(n); for(int i = 0; i < m; i++){ int a = readIntSp(1, n), b = readIntLn(1, n); assert(a != b); a--; b--; in[b]++; adj[a].push_back(b); out[a]++; } int ans = count(out.begin(), out.end(), 0) - 1; queue<int> q; for(int i = 0; i < n; i++){ if(in[i] == 0){ q.push(i); } } while(!q.empty()){ int u = q.front(); q.pop(); ord.push_back(u); for(int v : adj[u]){ if(--in[v] == 0){ q.push(v); } } } if(ord.size() < n) ans = -1; cout << ans << '\n'; } return 0; }