C :

#include<stdio.h>
#include<string.h>
#include<math.h>
char f[2000][20000];
void plus(int a){
int i,c=0,n;
for(i=0;i<strlen(f[a-1]);i++){
if(f[a-2][i]==0) n=f[a-1][i]-'0'+c;
else n=f[a-1][i]-'0'+f[a-2][i]-'0'+c;
f[a][i]=n%10+'0';
c=n/10;}
if(c) f[a][i]=c+'0';}

int main(){
int a,b;
while(scanf("%d%d",&a,&b)!=EOF){
int n=b-a,i;
memset(f,0,sizeof(f));
strcpy(f[0],"1");
strcpy(f[1],"1");
for(i=2;i<=n;i++) plus(i);
for(i=strlen(f[n])-1;i>=0;i--) printf("%c",f[n][i]);
puts("");}
return 0;}

C++ :

#include<iostream>
using namespace std;
int move(int n)
{
	if(1==n || 2==n)
		return 1;
	if(3==n) 
		return 2;
	else
	{
		return move(n-1)+move(n-2);
	}
}
int main()
{
	int m,n;
	cin>>m>>n;
	cout<<move(n-m+1)<<endl;
	return 0;
}