#include <fstream>
using namespace std;

ifstream f("fact.in");
ofstream g("fact.out");

int p,n,i,j,pr,ul,mid;

int factorial(int n){
    int p=5, x=0;
    while (p<=n){
        x+=n/p;
        p*=5;
    }
    return x;
}

int main(){
    f>>p;
    pr=1;
    ul=p*5;
    while(pr<=ul){
        mid=(pr+ul)/2;
        if(factorial(mid)>=p)
            ul=mid-1;
        else
            pr=mid+1;
    }
    if(factorial(pr)==p)
        g<<pr<<'\n';
    else
        g<<"-1\n";
    g.close();
    return 0;
}