#include <bits/stdc++.h>
using namespace std;
const int maxn = 100005, inf = 1e9 + 7;
int fa[maxn];
long long n, m, dp[maxn];
int sz[maxn], costs[maxn];
vector<int> fas;
bool vis[maxn];
int findfa(int x) {
  if (fa[x] == x)
    return x;
  else
    return fa[x] = findfa(fa[x]);
}
void bag(int wei, int val) {
  for (int i = n; i >= wei; i--) {
    dp[i] = min(dp[i], dp[i - wei] + val);
  }
}
bool check(int xx) {
  while (xx) {
    if ((xx % 10) != 4 && (xx % 10) != 7) {
      return 0;
    }
    if (xx < 10) break;
    xx /= 10;
  }
  return 1;
}
int main() {
  memset(dp, 1e9 + 7, sizeof(dp));
  cin >> n >> m;
  for (int i = 1; i <= n; i++) fa[i] = i;
  for (int i = 1; i <= m; i++) {
    int x, y;
    cin >> x >> y;
    fa[findfa(x)] = findfa(y);
  }
  for (int i = 1; i <= n; i++) {
    sz[findfa(i)]++;
  }
  for (int i = 1; i <= n; i++) {
    costs[sz[i]]++;
  }
  dp[0] = 0;
  for (int i = 1; i <= n; i++) {
    if (costs[i]) {
      for (int j = 1; j <= costs[i]; j <<= 1) {
        bag(j * i, j);
        costs[i] -= j;
      }
      bag(costs[i] * i, costs[i]);
    }
  }
  long long ans = 1e9 + 7;
  for (int i = 1; i <= n; i++) {
    if (check(i)) ans = min(ans, dp[i]);
  }
  if (ans == 1e9 + 7)
    cout << "-1" << endl;
  else
    cout << ans - 1 << endl;
  return 0;
}
