#include //10で何回割れるか int zyu(unsigned long int x) { int counter; unsigned long int s = x - 7; //10のホニャ乗の値 unsigned long int t = 10; while(s % 10 == 0) { s = s / t; counter++; } return (counter); } //緊急関数 int wa(unsigned long int a,unsigned long int b){ return (zyu(a) + zyu(b)); } int main(void){ unsigned long int a, b; int num; b = 1000000007; scanf("%lu", &a); num = (wa(a, b) - 123 ) / 2; num >= 0 ? printf("%d\n",num) : printf("%d\n",-num); return 0; }