#include <fstream>
using namespace std;
ifstream f("fact.in");
ofstream g("fact.out");
int P;
int Solve(int fin)
{
    int current=5,sol=0;
    while(current<=fin)
    {
        sol+=fin/current;
        current*=5;
    }
    return sol;
}
void Binary_Search()
{
    int st=1,dr=100000000,mid,sol=-1;
    while(st<=dr)
    {
        mid=(st+dr)/2;
        int aux=Solve(mid);
        if(aux<P)
            st=mid+1;
        if(aux>P)
            dr=mid-1;
        if(aux==P)
            sol=mid,dr=mid-1;
    }
    g<<sol<<"\n";
}
int main()
{
    f>>P;
    Binary_Search();
    return 0;
}