#include <fstream>

using namespace std;
ifstream f("fact.in");
ofstream g("fact.out");
int n;
long long st, dr, mid, sol, i;
bool zero(int x){
    int number_of_zeros = 0;
    while(x / 5 != 0){
        x = x / 5;
        number_of_zeros += x;
    }
    if(number_of_zeros >= n)
        return true;
    return false;
}
int main()
{   f >> n;
    st = 1; dr = 5 * n;
    while(st <= dr){
        mid = (st + dr) / 2;
        if(zero(mid) == 1){
            sol = mid;
            dr = mid - 1;
        }
        else
            st = mid + 1;
    }
    g << sol;
    return 0;
}