#include <fstream>

using namespace std;
ifstream f("fact.in");
ofstream g("fact.out");
long long zero(int x)
{
long long  s=0,p;
    p=5;
    while (p<=x)
    {
        s=s+x/p;
        p=p*5;
    }
    return s;
}
long long cautbin(int p)
{
    long long dr,step,j;
    dr=5*p;
    step=1;
    while (step<dr)
    {
        step<<=1;
    }
    for ( j=0;step;step>>=1)
    {
        if (j+step<=dr&&zero(j+step)<p)
        {
            j+=step;
        }
    }
    if (zero(j+1)!=p)
    {
        return -1;
    }
    return j+1;
}
int main()
{
   long long p;
    f>>p;
    g<<cautbin(p);
    return 0;
}