/*
B(x) = x
C(a) + C(b) = C(ab)
D(x) = C(x!)
x! = p1^a1*p2^a2*p3^a3....
https://cs.stackexchange.com/questions/138689/four-functions-problem
*/
int largestPower(int n, int p){
int x = 0;
while(n){
n/=p;
x+=n;
}
return x;
}
int main()
{
int n;
cin>>n;
vector<int> primes;
bool arr[n+1];
memset(arr, true, sizeof(arr));
for(int p=2;p*p<=n;p++){
if(arr[p] == true){
for(int i=p*p;i<=n;i+=p){
arr[i] = false;
}
}
}
for(int i=2;i<n;i++){
if(arr[i]){
primes.push_back(i);
}
}
int ans = 0;
for(int i=0;i<primes.size();i++){
ans+=(largestPower(n, primes[i]));
}
cout<<ans<<endl;
return 0;
}