#include <cstdio>
int main() {
    int k = 0;
    char a;

    while (scanf("%c", &a) != -1) {
        if ((a == '4') || (a == '7'))
            k++;
    }

    if ((k == 4) || (k == 7))
        printf("YES");
    else
        printf("NO");
    return 0;
}