C :

#include<stdio.h>
#include<string.h>
char a[100];
main()
{
	int i,s=1;
	gets(a);
	for(i=0;i<strlen(a);i++)
	{
		if(a[i]==a[i+1])
		{
			s++;	
		}
		else
		{
			if(s==1)
			{
				printf("%c",a[i]);
			}
			else
			printf("%d%c",s,a[i]);
			s=1;
		}
	}
}

Python :

a = input()
a = a + " "
s= 1
for i in range (0,len(a)-1):
    if a[i]==a[i+1]:
        s += 1
    else:
        if s != 1:
            print(s,end='')
        print(a[i],end='')
        s = 1