#include<fstream>
using namespace std;
ifstream in("fact.in");
ofstream out("fact.out");
long long a,b,n,k,x,v[200001],i,j,p,mid,dr,st,s,z,alfa;
int main(){
in>>p;
st=1;
dr=p*5;
alfa=-1;
while(st<=dr){
    mid=(dr+st)/2;
    s=0;
    for(i=5;i<=mid;i=i*5){
          s=s+mid/i;

    }
    if(s<p){
       st=mid+1;
    }
    if(s>=p){
        dr=mid-1;
    }

}
if(s==p)
out<<st;
else
    out<<alfa;

return 0;
}