#include <iostream>
#include <fstream>
#include <climits>
using namespace std;
ifstream fin("fact.in");
ofstream fout("fact.out");
int p;
int func(int nr){
    int sum = 0;
    for(int i = 5; i <= nr; i *= 5){
        sum += nr / i;
    }
    return sum;
}
void solve(){
    int l = 0, r = INT_MAX;
    while(l <= r){
        int mid = (l + r) / 2;
        int ans = func(mid);
        if(ans == p){
            mid = mid - mid % 5;
            fout << mid;
            return;
        }
        else if(ans > p){
            r = mid - 1;
            continue;
        }
        l = mid + 1;
    }
    fout << "-1";
}
int main()
{
    fin >> p;
    solve();
    return 0;
}