#include<bits/stdc++.h>
#define int long long
using namespace std;

int p,n;
bool u;

int check(int n) {
	int s=0;
	for (int i=5; i<=n; i*=5) s+=n/i;
	return s;
}

int32_t main() {
	ifstream cin("fact.in");
	ofstream cout("fact.out");
	cin>>p;
	int st=0, dr=1e9;
	
	while (st<=dr) {
		int mid=(st+dr)/2;  
		int a=check(mid);
		if (a==p) u=1;
		if (a>=p) dr=mid-1;
		else {
			st=mid+1; 
		}
	}
	if (p==0) cout<<"1";
	else
	if (u) cout<<dr+1;
	else cout<<"-1";

	
	
	return 0;
}