#include <fstream>

using namespace std;
ifstream cin("fact.in");
ofstream cout("fact.out");
int main()
{
    int p, st=1, dr=1e9, mij, aux, k=1, zero=0, sol=-1;
    cin>>p;
    while(st<=dr)
    {
        mij=(st+dr)/2;
        k=5;
        while(mij>=k)
        {
            zero+=mij/k;
            k=k*5;
        }
        if(zero<p)
        {
            st=mij+1;
        }
        else if(zero>=p)
        {
            sol=mij;
            dr=mij-1;
        }
        zero=0;
    }
    cout<<sol;
}