#include <fstream>

using namespace std;

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

bool ok=0;

int nr0(int n)
{
    long long p=5;
    int s=0;
    while(p<=n)
    {
        s+=n/p;
        p*=5;
    }
    return s;
}

int rezolva(int p)
{
    int s=1,d=2000000000,m,x;

    while(s<=d)
    {
        m=(s+d)/2;
        x=nr0(m);
        if(x==p)
            ok=1;
        if(x>=p)
            d=m-1;
        else s=m+1;
    }
    if(ok)
        return s;
    return -1;
}

int main()
{
int p;

f>>p;
g<<rezolva(p);

    return 0;
}