#include <cstdio>
#include <cmath>
using namespace std;
long long nrz(long long n);
int n, j;
int main() {

    freopen("fact.in", "r", stdin);
    freopen("fact.out", "w", stdout);
    scanf("%d", &n);
    for (j = 5; nrz(j) <= n; j = j + 5);
    if (nrz(j - 5) == n)
        printf("%d", j - 5);
    else printf("-1");
    return 0;
}
long long nrz(long long n) {
    long long num = 0, mod = 5;
    while (n / mod != 0) {
        num = num + n / mod;
        mod = mod * 5;
    }
    return num;
}