#include <fstream>
const std::string programName = "fact";
std::ifstream f(programName + ".in");
std::ofstream g(programName + ".out");
int nr(int);
void binary(int, int, int);
int main() {
    int P;
    f >> P;
    binary(0, 1e9, P);
    return 0x0;
}
int nr(int k) {
    int cnt = 0;
    for (int i = 5; i <= k; i *= 5)
        cnt += k/i;
    return cnt;
}
void binary(int left, int right, int P) {
    while (left < right) {
        int mid = (left + right) >> 1;
        if (nr(mid) >= P)
            right = mid;
        else
            left = mid + 1;
    }
    if (nr(left) == P)
         g << left;
    else
        g << -1;
}