#include<fstream>
using namespace std;
ifstream fin("fact.in");
ofstream fout("fact.out");

unsigned long long zero(unsigned long long nr){
    unsigned long long nrZero = 0;
    while(nr){
        nrZero += nr/5;
        nr/=5;
    }
    return nrZero;
}
unsigned long long fact(unsigned long long p){
    unsigned long long hi = 1<<30,rez,lo=0,mid;
    if(p == 0) return 1;

    while(hi - lo > 1){
        mid = lo + (hi-lo)/2;
        rez = zero(mid);
        if(p == rez)  return mid;
        else if(p < rez) hi = mid - 1;
        else lo = mid + 1;
    }
    return 0;
}
int main(){
    unsigned long long rezFinal,p;
    fin>>p;
    rezFinal = fact(p);
    if(rezFinal > 5){
        fout << rezFinal - rezFinal%5<<"\n";
    } else if(rezFinal) fout << rezFinal<<"\n";
    else fout << "-1\n";
    fin.close();
    fout.close();
    return 0;
}