#include<stdio.h>
int main()
{
    int n;
    int count=0;
    scanf("%d",&n);
    while(n!=0)

    {

        n=n/10;
        if(n==4 || n==7)
            count++;

    }

    while(count!=0)
    {
        count=count/10;
        if(count!=4 || count!=7)
            continue;
        }














    return 0;
}