#include <fstream>
using namespace std;
ofstream out("fact.out");
ifstream in("fact.in");
int p;
int catiDeZero(long long n)
{
    int nr = 0;
    while(n>0)
    {
        nr+=n/5;
        n/=5;
    }
    return nr;
}

int cautbin(int st, int dr)
{
    int mid = (st+dr)/2;
    if(st == dr)
        return -1;
    int k = catiDeZero(mid);
    if(k==p && catiDeZero(mid-1) < k)
        return mid;
    if(k<p)
        return cautbin(mid,dr);
    if(k>=p)
        return cautbin(st,mid);
}

int main()
{
    int st = 1, dr = 1000000000;
    in >> p;
    if(p == 0) out << 1;
    else
    out << cautbin(st,dr);
    //out << catiDeZero(200000000);
    return 0;
}