a.cpp

#include <bits/stdc++.h>
using namespace std;
#define IOS                           \
    ios_base::sync_with_stdio(false); \
    cin.tie(NULL);                    \
    cout.tie(NULL);
#define pii <pair<int,int>
#define vi vector<int>
#define vp vector<pair<int, int>>
#define vpp vector<pair<pair<int, int>, int>>
#define si set<int>
#define ll long long
#define ld long double
#define pqf priority_queue<int, vector<int>>
#define pqb priority_queue<int, vector<int>, greater<int>>
#define ps(x, y) fixed << setprecision(y) << x
#define MOD 1e9
#define PI 3.1415926535

void swap(int *a, int *b)
{
    int temp = *a;
    *a = *b;
    *b = temp;
}
int arraySum(int a[], int n)
{
    int initial_sum = 0;
    return accumulate(a, a + n, initial_sum);
}

void solve()
{
     string s;
    int k=0;
    cin>>s;
    for (int i = 0; i < s.length(); i++)
    {
        if((s[i]=='4')||s[i]=='7'){
            k++;
            
        }
 
    }
    cout<<(k==4||k==7?"YES":"NO");
}

int main()
{
    IOS
#ifndef ONLINE_JUDGE
        freopen("input.txt", "r", stdin);
    freopen("output.txt", "w", stdout);
#else
#endif
    // int t;
    // cin >> t;
    // while (t--)
        solve();
    return 0;
}