#include<fstream>
using namespace std;
ifstream fin("fact.in");
ofstream fout("fact.out");
long long p,mid,st,dr;
long long expo(long long p){
    long long x=5;
    long long sol=0;
    if(x>p){
        return 0;
    }
    while(x<=p){
        sol+=p/x;
        x*=5;
    }
    return sol;
}
int main(){
    fin>>p;
    st=1;
    dr=2000000000LL;
    while(st<=dr){
        mid=(st+dr)/2;
        if(expo(mid)>=p){
            dr=mid-1;
        }
        else{
            st=mid+1;
        }
    }
    if(expo(st)>p){
        fout<<"-1";
        return 0;
    }
    fout<<st;
    return 0;
}