Solution of 110A. Nearly Lucky Number (Codeforces)

#include<iostream>
#include<cstdio>
#include<cmath>
#include<cstring>
using namespace std;
typedef long long ll;

int main()
{
    string s;
    cin >> s;
    ll len = s.length();
    ll count =0;
    for(int i=0; i<len; i++)
    {
        if(s[i]=='7' || s[i]=='4')
        {
            count++;
        }
    }
    if(count == 4 || count == 7)
    {
        cout << "YES" << endl;
    }
    else
    {
        cout << "NO" << endl;
    }

}