import java.util.Scanner;
public class Main{
public static void main
(String[] args
){ Scanner sc
= new Scanner
(System.
in); int c=0;
for(int i=0;i<rs.length();i++){
if(rs.charAt(i) == '4' || rs.charAt(i) == '7'){
c++;
}
}
System.
out.
println((c
==4 || c
==7)?"YES":"NO"); }
}
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