#include <bits/stdc++.h>
using namespace std;
int main() {
int c=0;
string s;
cin >> s;
for(int i=0;i<s.size();i++)
{
if(s[i]=='4' || s[i]==7)
c++;
}
if(c==4 || c==7)
{
cout << "YES" << endl;
}
else
{
cout << "NO" << endl;
}
return 0;
}
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