#include <bits/stdc++.h>

using namespace std;

ifstream fin("fact.in");
ofstream fout("fact.out");
int n, st, dr, mij, c, z, r;

int main() {
    fin >> n;
    st = 1;
    dr = 1e9;
    while(st <= dr) {
        mij = st + (dr - st) / 2;
        c = mij;
        z = 0;
        while(c >= 5) {
            c /= 5;
            z += c;
        }
        if(z >= n) {
            r = mij;
            dr = mij - 1;
        }
        else st = mij + 1;
    }
    fout << r;
}