#include <stdio.h>
main()
{
    int t,x; 
    float sum;
    t=0;
    sum=0;
    scanf("%d",&x);
    if(x==-1)
    {
        printf("无数据");
    }
    else{
         
    while (x!=-1)
    {
    sum+=x;
    t++;
    scanf("%d",&x);
    }
    printf("%0.2f", sum/t);
    }
}