#include <stdio.h>

int main(void)
{
	int n=3;
	int i;
	int age,sum=0;
	double c=0.0;
	for(i=0;i<n;i++){
		scanf("%d",&age);
		if(age>=15&&age<=25){
		sum=sum+age;
		c++;
		}
	}
	double b;
	b=sum/c;
	printf("%0.2f",b);
	return 0;
 }