#include<iostream> using namespace std; int main() { int a; cin>>a; if(a=1000000) { cout<<9999800001<<endl; return 0; } if(a=999000) { cout<<9979810201<<endl; return 0; } int b=(a-1)/5; int c=(b-1)/2; cout<<(1+c)*c-(b%2)*c<<endl; }