#include <fstream>
using namespace std;
int main()
{
    ifstream fin("fact.in");
    ofstream fout("fact.out");
	int n,li=1,lf=500000000,m,r,no=0,a=-1,p;
    fin>>n;
	while(li<=lf)
	{
		no=0;
		m=(li+lf)/2;
		for(r=5;r<=m;r*=5){no+=m/r;}
		if(no==n)
		{a=m;
		lf=m-1;}
		if(no>n)
            lf=m-1;
        if(no<n)
            li=m+1;

	}
    fout<<a;
	return 0;
}