#include <stdio.h>
#define for_i(i, range, inner)                                                 \
    {                                                                          \
        int i;                                                                 \
        for (i = 0; i < range; i++)                                            \
            inner;                                                             \
    }

int main() {
    int n, cnt;
    scanf("%d", &n);
    for_i(i, n + 1, {
        int a = i;
        while (a != 0) {
            if (a % 10 == 2) {
                cnt++;
            }
            a /= 10;
        }
    });
    printf("%d", cnt);
    return 0;
}