#include <iostream>
#include <stack>
#include <vector>
#include <bitset>
auto *in = fopen("sortaret.in", "r") ;
auto *out = fopen("sortaret.out", "w") ;
const int maxn = 5e4 ;
std::vector<int> G[1 + maxn] ;
std::vector<int> F[1 + maxn] ;
std::stack<int> sol ;
std::vector<int> curr ;
std::bitset<1 + maxn> seen1, seen2 ;
void dfs1(int node) {
seen1[node] = 1;
for (auto it : G[node]) {
if (!seen1[it]) {
dfs1(it) ;
}
}
sol.push(node) ;
}
void dfs2(int node) {
seen2[node] = 1;
for (auto it : F[node]) {
if (!seen2[it]) {
dfs2(it) ;
}
}
curr.push_back(node) ;
}
int main() {
int n, m, x, y ;
fscanf(in, "%d %d", &n, &m) ;
for (int i = 1 ; i <= m ; ++ i) {
fscanf(in, "%d %d", &x, &y) ;
G[x].push_back(y) ;
F[y].push_back(x) ;
}
for (int i = 1 ; i <= n ; ++ i) {
if (!seen1[i]) {
dfs1(i) ;
}
}
std::vector<std::vector<int> > ret ;
while (!sol.empty()) {
if (!seen2[sol.top()]) {
curr.clear() ;
dfs2(sol.top());
ret.push_back(curr) ;
}
sol.pop() ;
}
fprintf(out, "%d\n", ret.size()) ;
for (auto it : ret) {
for (int i = it.size() - 1 ; i >= 0 ; -- i) {
fprintf(out, "%d ", it[i]) ;
}
fputc('\n', out) ;
}
}