Codeforces_110A

//Codeforces Round 110A
#include <string>
#include <cstring>
#include <iostream>
using namespace std;
int main()
{
    int len, answ=0;
    string s;
    char mass[101];
    cin >> s;
    len = s.size();
    strcpy(mass, s.c_str());
    for(int i=0;i<len;i++)
    {
        if(mass[i]=='4' || mass[i]=='7'){answ++;}
    }
    if(answ==4 || answ==7 || answ==47 || answ==74){cout<<"YES";}
    else{cout<<"NO";}
    return 0;
}