#include <fstream>
#include <cmath>
using namespace std;
long long nrz(int n);
int n, j;
int main() {
    ifstream ifs("fact.in");
    ofstream ofs("fact.out");
    ifs >> n;
    for (j = 5; nrz(j) <= n; j = j + 5);
    if (nrz(j - 5) == n)
        ofs << j - 5;
    else ofs << -1;
    return 0;
}
long long nrz(int n) {
    int i = 1;
    long long num = 0;
    while (n / pow(5, i) != 0) {
        num = num + n / pow(5, i);
        i++;
    }
    return num;
}