#include <bits/stdc++.h>
#define loop(i,a,b) for(int i=a;i<=b;i++)
#define ll long long
#define ar array
#define INF 1e9
#define ln '/n'
///folosesti scanf si printf!!!
using namespace std;
ifstream f("fact.in");
ofstream g("fact.out");
int n;
int main(){
f>>n;
if(!n){g<<1;return 0;}
int l=1,r=500000000,ans=0;
while(l<=r){
    int mid=(l+r)/2;
    int x=mid,cnt=0;
    while(x)cnt+=(x/5),x/=5;
    if(cnt==n)ans=mid,r=mid-1;
    else if(cnt>n)r=mid-1;
    else l=mid+1;
}
if(!ans){g<<-1;return 0;}
g<<ans;
}