#include <bits/stdc++.h>
#define ll 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=1e19,mid;
ll realpoz=-1;
while(st<=dr){
    mid=(st+dr)/2;
    ll curr_sum=sum(mid);
    if(curr_sum==p)
        return mid;
    if(curr_sum>p)
        dr=mid-1;
    else st=mid+1;
}
return -1;
}
int main()
{
    freopen("fact.in","r",stdin);
    freopen("fact.out","w",stdout);
    scanf("%lld ",&p);
    printf("%lld",bin());
}