#include <fstream>
#include <climits>
using namespace std;

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

long long int zeros(long long int val){
    long long int ex = 0;
    long long int p=5,pp=5;
    while(val >= pp){
        ex += val/pp;
        pp *= p;
    }
    return ex;
}

int main(){

    long long int n;
    fin>>n;
    long long int st = 1, dr = LONG_LONG_MAX,pos=-1;
    while(st <= dr){
        long long int mij = st+(dr-st)/2;
        long long int zero = zeros(mij);
        if(zero == n){
            pos = mij;
        }
        if(zero >= n) dr = mij-1;
        else st = mij+1;
    }
    fout<<pos;

}