#include <bits/stdc++.h>

using namespace std;

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

long long Nr;

long long nz(int x){
    if(x == 0) return 1;

    long long n = 0;
    for(int i = 5;x / i >= 1; i *= 5){
        n += x / i;
    }
    return n;
}

int cb(int st, int dr, long long val){
    int answ = -1;
    while(st <= dr){
        int mij = (st + dr) / 2;
        long long zero = nz(mij);

        if(zero >= val){
            answ = mij;
            dr = mij - 1;
        }
        else st = mij + 1;
    }

    return (nz(answ) > val) ? -1 : answ;
}

int main(){

    f >> Nr;
    g << cb(1, 1000000000, Nr);
}