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#include <iostream>
using namespace std;
char prime[2000002];
int main()
{
int i, j, n, cnt = 0;
FILE *in, *out;
in = fopen("ciur.in", "r");
out = fopen("ciur.out", "w");
fscanf(in, "%d", &n);
for (i = 2; i <= n; i+=2){
prime[i] = 1;
}
cnt++;
for (i = 3; i <= n; i++){
if (prime[i] == 0){
cnt++;
for (j = i*i; j <= n; j+=i){
prime[j] = 1;
}
}
}
fprintf(out, "%d", cnt);
return 0;
}