#include <fstream>

using namespace std;
ifstream in("fact.in");
ofstream out("fact.out");

long long zero(long long x)
{
    long long sum=0;
    for (long long i=5; i<=x; i*=5)
        sum+=(x/i);
    return sum;
}
int main()
{
    long long p,inc,sf,mij;
    in>>p;
    inc=1;
    sf=5*p;
    while (inc<=sf)
    {
        mij=(inc+sf)/2;
        if(zero(mij)<p)
            inc=mij+1;
        else sf=mij-1;
    }
    if (zero(inc)==p) out<<inc;
    else out<<-1;
    return 0;
}