#include <fstream>

using namespace std;

long long k, p, u;

long long zero(long long n){
    long long p = 5, s = 0;
    while (p <= n) {
        s += n/p;
        p *= 5;
    }
    return s;
}

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


    fin >> k;
    p = 1; u = 5*k;

    while (p <= u) {
        long long mid = (p+u)/2;

        if ( zero(mid) >= k )
            u = mid - 1;
        else
            p = mid + 1;
    }

    if (zero(p) == k)
        fout<<p;
    else
        fout<<-1;

    return 0;
}