#include <cstdio>

using namespace std;

int caut_bin(int *A, int len, int value) {
    int poz = 0; int pas = 1<<4;
    while (pas >>= 1)
        if ((pas + poz < len) && (A[pas + poz] <= value))
            poz += pas;

    return poz;
}

int main() {
    freopen("fact.in", "r", stdin);
    freopen("fact.out", "w", stdout);

    int N;
    scanf("%d", &N);

    int v[16], v_len = 0;
    for (int k = 1; k <= N; k *= 5) {
        v[v_len] = k;
        v_len++;
    }

    for (int i = 5; i <= N; i += 5) {
        N -= caut_bin(v, v_len, i);
    }

    printf("%d", 5*N);

    return 0;
}