#include <iostream>
#include <fstream>
using namespace std;
ifstream in("fact.in");
ofstream out("fact.out");
inline int nrn(int n)
{
    int nr=0;
    while(n > 0) {
        nr = nr + n/5;
        n = n/5;
    }
    return nr;
}
inline int bin(int p)
{
    int st=1;
    int dr=(1 << 30);
    int a;
    int k=-1;
    while(st<=dr)
    {
        a=(st+dr)/2;
        int b = nrn(a);
        if(b<p)
            st=a+1;
        else if(b>=p) {
            dr=a-2;
            if(b == p)
                k = a;
        }
    }
    return k;
}
int main()
{
    int p;
    in>>p;
    out<<bin(p);
    return 0;
}