#include <bits/stdc++.h>
#define ll unsigned long long int
using namespace std;
ll p;
vector <ll> q;
static inline ll sum(ll val){
ll curr=0;
for(ll x=5;x<=val;x*=5)
    curr+=(val/x);
return curr;
}
static inline ll bin(){
ll st=1,dr=1000000002,mid;
ll realpoz=-1;
while(st<=dr){
    mid=(st+dr)/2;
    ll curr_sum=sum(mid);
    if(curr_sum>=p)
        dr=mid-1,realpoz=(curr_sum==p?mid:realpoz);
    else st=mid+1;
}
return (realpoz==-1?st:realpoz);
}
int main()
{
    freopen("fact.in","r",stdin);
    freopen("fact.out","w",stdout);
    scanf("%llu ",&p);
    printf("%llu ",bin());
}