#include <fstream>

using namespace std;

ifstream in ("fact.in");
ofstream out ("fact.out");

int nrc0 (int n){
    long long p=5;
    int cnt = 0;
    while (p<=n)
        cnt += n/p, p*=5;
    return cnt;
}

int main()
{
    int n;
    in >> n;
    if (n==0){
        out << 0;
        return 0;
    }
    int l=1, r=10e9, mid;
    while (l<r){
        mid = (l+r)/2;
        int nrc = nrc0(mid);
        if (nrc >= n)
            r = mid;
        else
            l = mid + 1;
    }
    out << r;
    return 0;
}