Y - Nearly Lucky Number CodeForces - 110A
Petya loves lucky numbers. We all know that lucky numbers are the positive integers whose decimal representations contain only the lucky digits 4 and 7. For example, numbers 47, 744, 4 are lucky and 5, 17, 467 are not.
Unfortunately, not all numbers are lucky. Petya calls a number nearly lucky if the number of lucky digits in it is a lucky number. He wonders whether number n is a nearly lucky number.
Input
The only line contains an integer n (1 ≤ n ≤ 1018).
Please do not use the %lld specificator to read or write 64-bit numbers in С++. It is preferred to use the cin, cout streams or the %I64d specificator.
Output Print on the single line "YES" if n is a nearly lucky number. Otherwise, print "NO" (without the quotes). Examples
Input
40047
Output
NO
Input
7747774
Output
YES
Input
1000000000000000000
Output
NO
Note
In the first sample there are 3 lucky digits (first one and last two), so the answer is "NO".
In the second sample there are 7 lucky digits, 7 is lucky number, so the answer is “YES”.
In the third sample there are no lucky digits, so the answer is "NO
問題簡述：這個問題是要求你判斷一個數字的幸運數4和7加起是否等於4或者7。等於，就輸出"YES";不等於，就輸出"NO"。
問題思路：構造一個空的字串，然後輸入數字；判斷4和7加起來是否等於4或7。
程式說明：本程式使用了string n來構造空字串。
#include<iostream>
#include<string>
using namespace std;
int main()
{
int n = 0;
string a;
cin >> a;
int m = a.length();
for (int i = 0; i <m; i++)
{
if (a[i] == '4' || a[i] == '7') n += 1;
}
if (n == 4 || n == 7) cout << "YES";
else cout << "NO";
return 0;
}