#include <fstream>
using namespace std;
ifstream f("fact.in");
ofstream g("fact.out");
long long k,n,e;
long long p;
int main() {
    
 
    f>>p;
    n = 4*p, k = 0; e = 5;
    while(n/e) k += n/e, e *= 5;
    n = 5*(n/5+1);
    do {
        e = 5, k = 0;
        while(n/e) k += n/e, e *= 5;
        n += 5;
    } while(k < p);
    n -= 5;
    if(p == 0) g<<1;
    else {
        if(k == p) g<<n;
        else g<<-1;
    }
    return 0;
}