#include<fstream>
using namespace std;
inline int fact(int x){
	return (x==1 ? x : x*fact(x-1));
}
int nr_zero_fact(int n){
	int q=1,c=1,s=0;
	while(q!=0){
		q=(int)floor((double)(n/(int)pow((double)5,(double)c)));
		s+=q;
		c++;
	}
	return s;
}
int main(){
	ifstream in("fact.in");
	ofstream out("fact.out");
	int p,x=1;
	in>>p;
	while(nr_zero_fact(x)!=p) x++;
	out<<x;
	return 0;
}