#include <iostream>
#include <cstdio>
using namespace std;
int zero(int n) {
	int p=5,s=0;
	while(n/p!=0) {
		s+=n/p;
		p*=5;
	}
	return s;
}
int main()
{
	freopen("fact.in","r",stdin);
	freopen("fact.out","w",stdout);
    int n,st,dr,mij,elem=-1,z;
    scanf("%d",&n);
    if(n==0) {
		cout<<1;
		return 0;
	}
    st=0;
    dr=5*n;
    while(st<=dr) {
		mij=(st+dr)/2;
		z=zero(mij);
		if(z>n)
			dr=mij-1;
		else {
			if(z<n)
				st=mij+1;
			else {
				elem=mij;
				dr=mij-1;
			}
		}
    }
	cout<<elem;


    return 0;
}