#include <fstream>
using namespace std;
 
int find(int p) {
    int i = 0;
    int aux = 0;

    do {
        i++;
        aux = i;
        while (aux % 5 == 0){
            p--;
            aux = aux / 5;
        }
        if (p < 0)
            return -1;
    } while (p > 0);

    return i;
}

int main() {
    ifstream fin("fact.in");
    ofstream fout("fact.out");
    int p;
    fin>>p;

    int n = find(p);

    fout<<n;
    return 0;
}