C :

#include<stdio.h>
#include<string.h>
char a[20],b[20];
int main(){
	scanf("%s%s",&a,&b);
	int ah = (a[0]-'0')*10+a[1]-'0';
	int am = (a[3]-'0')*10+a[4]-'0';
	int as = (a[6]-'0')*10+a[7]-'0';
	
	int bh = (b[0]-'0')*10+b[1]-'0';
	int bm = (b[3]-'0')*10+b[4]-'0';
	int bs = (b[6]-'0')*10+b[7]-'0';
	
	int at=ah*3600+am*60+as;
	int bt=bh*3600+bm*60+bs;
	
	printf("%d",at-bt);
	return 0;
}

Python :

a = input()
b = input()
x = a.split(':')
y = b.split(':')
c = int(x[0]) * 3600 + int(x[1]) * 60 + int(x[2]) -  int(y[0])*3600 - int(y[1])*60 - int(y[2])
print(c)