# include<iostream> # include<cmath> using namespace std; bool isprimes[5000001]={}; int primes[5000001]={}; int n = 0, j = 0; int main(){ int x; cin>>x; for(int i = 2; i <= x; i++){ if(isprimes[i]==0){ primes[n]=i; n++; } j = 0; do{ isprimes[i*primes[j]]=1; if(i%primes[j]==0)break; j++; }while(i*primes[j]<=x); } cout<<n; return 0; }