#include <stdio.h>

int main(void){
	long long int n;
	scanf("%lld",&n);
	if(n < 10 || n%10 != 3){
		printf("-1");
	}else{
		int count = 0;
		while(n > 10){
			n = n/10;
			count++;
		}
		printf("%d",count);
	}
}