C :

#include <stdio.h>

main(){
   int n,i,sum;
   while (1 == scanf("%d",&n) && n) {
      sum = n;
      for (i=2;i*i <= n;i++) {
         if (n%i == 0) {
            sum -= sum/i;
         }
         while (n%i == 0) n /= i;
      }
      if (n > 1) sum -= sum/n;
      printf("%d\n",sum);
   }
}

C++ :

#include <stdio.h>
unsigned eulerFunc(unsigned n)
{
	unsigned ans = 1;
	for (unsigned i = 2; i*i <= n; i++)
	{
		if (n % i == 0)
		{
			n /= i, ans *= (i-1);
			while (n % i == 0) n /= i, ans *= i;//把质数除去，巧妙变相分解质因子
		}
	}
	if (n > 1) ans *= (n-1);
	return ans;
}
int main()
{
	int n;
	while (scanf("%d", &n) && n !=0)
	{
		printf("%d\n", eulerFunc(n));
	}
	return 0;
}