Display the characters in prime position

Write a program to display the characters in prime position of a given string.

Sample Input
Computer
Sample Output
o m u e

#include<stdio.h>
#include<string.h>
int main() {
  char str[50];
  int i, j;
  fgets(str,50,stdin);
  for(i=2;i<=strlen(str);i++){
    for(j=2;j<=i/2;j++){
      if(i%j==0){
        break;
      }
    }
    if(j>i/2)
      printf("%c ",str[i-1]);
  }
  return 0;
}