110A - Nearly Lucky Number

#include <iostream>
#include<string>
using namespace std;
int main() {

string s;
cin>>s;
int cnt=0;

for(int i=0;i<s.size();i++){
    if(s[i]=='7' || s[i]=='4')
    cnt++;
}
if (cnt==7 || cnt==4)
cout<<"YES";

else
cout<<"NO";

    return 0;
}