#include <bits/stdc++.h>
using namespace std;

ifstream fin("fact.in");
ofstream fout("fact.out");
unsigned long long desc(unsigned long long k1){
    unsigned long long sum = 0;
    while(k1 >= 5){
        k1 /= 5;
        sum += k1;
    }
    return sum;
}

int n;
unsigned long long st = 0, dr = 99999999999, gasit = 0, mij, k;

int main(){

    fin >> n;
    while(st <= dr && gasit == 0){
        mij = (st + dr) / 2;
        k = desc(mij);
        
        if(n == k) gasit = mij;
        else if(n < k) dr = mij - 1;
        else st = mij + 1;
    }
    fout << gasit;
}