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

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

long long int zeros(long long int val){
    return (val/5)+(val/25);
}

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;
        if(zeros(mij) >= n){
            pos = mij;
            dr = mij-1;
        }
        else st = mij+1;
    }
    if(pos%25 == 0)fout<<-1;
    else fout<<pos;

}