110A.cpp

#include<iostream>
using namespace std;

int main(){
  long long n;
  cin>>n;
  int check = 0;
  int rem;
  while(n != 0){
    rem = n%10;
    n /= 10;
    if(rem == 7 || rem == 4){
      check++;
    }

  }
  if(check != 4 && check != 7){
    cout<<"NO";
  }
  else{
    cout<<"YES";
  }
  return 0;
}