#include <bits/stdc++.h>

using namespace std;

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

int n;

int zerouri(int n) {
    int p=5,s=0;
    while(n/p!=0) {
        s+=n/p;
        p*=5;
    }
    return s;
}

int main()
{
    in >> n;
    int x = -1;
    for (int b = 5*n; b >= 1; b /= 2) {
        while (zerouri(x+b)<n) x += b;
    }
    int k = x+1;
    out << k;
    return 0;
}