#include <cstdio>
const int N = 1000000;
int p[N],int pN[N];
main(){p[0]=0;p[1]=0;int i,k,n,c;
for(i=2;i<N;i++)prime[i]=1;for(i=2;i*i<N;){for(k=2;i*k<N;k++)p[i*k]=0;do{i++;}while(!p[i]);}for(i=0,c=0;i<N;i++){p[i]&&c++;pN[i] = c;}for(;scanf("%d",&n)+1;printf("%d\n",pN[n]));}