#include<iostream>
using namespace std;
long ans=0;
int n,t;
int mod[12]={1,5,25,125,625,3125,15625,78125,390625,1953125,9765625};
int main(){
    cin>>n;
    if(n<5){
        cout<<0;
        return 0;
    }
    for(int i=5;i<=n;i++){
        ans+=i/5;
        for(int j=1;j<=11;j++){
            if(j>mod[i]){
                ans+=j;
            }
        }
    }
    cout<<ans;
}