#include <fstream>

 using namespace std;

 ifstream fin("fact.in");
 ofstream fout("fact.out");

 long long zerouri(long long n){
     long long sum = 0, p = 5;
     while(p <= n){
        sum += n / p;
        p *= 5;
     }
     return sum;
 }
 long long CautBin(long long n){
     long long st = 1, dr = 1000000000, rez = -1;
     while(st <= dr){
        long long mij = (st + dr) / 2;
        if(zerouri(mij) > n)
            dr = mij - 1;
        else if(zerouri(mij) == n){
            rez = mij;
            dr = mij - 1;
        }
        else
            st = mij + 1;
     }
     return rez;
 }

 int main(){

    long long n;
    fin >> n;
    fout << CautBin(n);

    return 0;
 }